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Molybdenum and tungsten oxo 2-adamantylidene (Adene) complexes that contain two nonafluoro-tert-butoxide (ORF9) ligands have been prepared through addition of 2-methylene- or 2-ethylideneadamantane...

Addition of 2-adamantylMgBr in diethyl ether to Mo(NArF)2(Cl)2(DME) (ArF = C6F5) gave Mo(NArF)2(Ad)2 (2, Ad = 2-adamantyl, DME = 1,2-dimethoxyethane). Addition of HCl and 2,2′-bipyridyl (bipy) to 2...

Addition of 1 equiv of water to Mo­(CArp)­(ORF9)3 (Arp = p-methoxyphenyl; ORF9 = OC­(CF3)3) in the presence of 5% NEt3 (vs Mo) in THF led to the formation of Mo­(O)­(CHArp)­(ORF9)2(THF)2 in good yield. Mo­(O)­(CHArp)­(ORF9)2(THF)2 reacts with 2 equiv of LiOHMT (OHMT = O-2,6-mesityl2C6H3) at room temperature to yield Mo­(O)­(CHArp)­(OHMT)2 and with 2 equiv of NaOTPP (OTPP = 2,3,5,6-tetraphenylphenoxide) to yield Mo­(O)­(CHArp)­(OTPP)2. In the presence of TMEDA (2.5 equiv), Mo­(CR)­(ORF9)3 (R = Arp, mesityl, or t-Bu) reacts with 1 equiv of water to yield Mo­(O)­(CHR)­(ORF9)2(TMEDA) complexes, from which (when R = t-Bu) TMEDA is readily displaced by 2,2′-bipyridyl to give Mo­(O)­(CH-t-Bu)­(ORF9)2(bipy). Mo­(O)­(CH-t-Bu)­(ORF9)2(bipy) was converted into Mo­(O)­(CH-t-Bu)­Cl2(bipy) readily, from which Mo­(O)­(CH-t-Bu)­Cl­(OHMT)­(3-Brpy) (3-Brpy = 3-bromopyridine) and Mo­(O)­(CH-t-Bu)­Cl­(OHIPT)­(3-Brpy) (OHIPT = O-2,6-(2,4,6-i-Pr3C6H2)2C6H3) were prepared. X-ray studies were carried out on Mo­(O)­(CHArp)­(ORF9)2(THF)2, Mo­(O)­(CH-t-Bu)­(ORF9)2(TMEDA), Mo­(O)­(CHArp)­(OTPP)2, Mo­(O)­(CH-t-Bu)­Cl­(OHMT)­(3-Brpy), and Mo­(O)­(CH-t-Bu)­Cl­(OHIPT)­(3-Brpy).

Addition of 2-adamantylMgBr in diethyl ether to Mo(NAr)2(Cl)2(DME) (Ar = 2,6-i-Pr2C6H3) gave Mo(NAr)2(2-Ad)2 (2-Ad = 2-adamantyl, DME = 1,2-dimethoxyethane), from which Mo(NAr)(Adene)(OTf)2(DME) (1...

Zn(DCTC) (DCTC = 3,6-dichlorodithiacatecholate) reacts with Mo(NAd)(CHCMe2Ph)Cl2(PPh2Me) (Ad = 1-adamantyl) to give Mo(NAd)(CHCMe2Ph)(DCTC)(PPh2Me). The reactions between Zn(DCTC) and Mo(NAd)(CH-t-Bu)(OTf)2(dme) or Mo(NAr)(CHCMe2Ph)(OTf)2(dme) (Ar = 2,6-i-Pr2C6H3; OTf = triflate; dme = 1,2-dimethoxyethane) produce [Mo(NAd)(CH-t-Bu)(DCTC)]2 and [Mo(NAr)(CHCMe2Ph)(DCTC)]2, respectively. Complexes that contain a 3,3′,5,5′-tetrasubstituted dithiabiphenolate were prepared in a reaction between Mo(NAr)(CHCMe2Ph)(Me2pyr)2 (Me2pyr = 2,5-dimethylpyrrolide) and the 3,3′,5,5′-tetrasubstituted dithiabiphenols, (3,3′,5,5′-tetrachlorodithiabiphenol (H2Cl4S2), 3,3′,5,5′-tetrabromodithiabiphenol (H2Br4S2), and 3,3′,5,5′-tetra-t-Bu-dithiabiphenol (H2Bu4S2)). The isolated complexes include Mo(NAr)(CHCMe2Ph)(Cl4S2)(pyridine), Mo(NAr)(CHCMe2Ph)(Br4S2)(pyridine), Mo(NAr)(CHCMe2Ph)(Bu4S2)(PMe3), and [Mo(NAr)(CHCMe2Ph)(Cl4S2)]2. Only the dithiabiphenolate derivatives (in the presence of B(C6F5)3) show activity for the metathesi...

Reactions between (Z)-XCH═CHX, where X = Cl, CF3, CN, and Mo(N-t-Bu)(CH-t-Bu)(OHIPT)Cl(PPh2Me) (OHIPT = O-2,6-(2,4,6-i-Pr3C6H2)2C6H3) produce Mo(N-t-Bu)(CHX)(OHIPT)Cl(PPh2Me) complexes. Addition of 2,2′-bipyridyl (Bipy) yields Mo(N-t-Bu)(CHX)(OHIPT)Cl(Bipy) complexes, which could be isolated and structurally characterized. The reaction between Mo(N-t-Bu)(CH-t-Bu)(OHMT)Cl(PPh2Me) (OHMT = O-2,6-(2,4,6-Me3C6H2)2C6H3) and (Z)-ClCH═CHCl in the presence of Bipy produces a mixture that contains both Mo(N-t-Bu)(CHCl)(OHMT)Cl(PPh2Me) and Mo(N-t-Bu)(CHCl)(OHMT)Cl(Bipy), but the relatively insoluble product that crystallizes from toluene-d8 is the phosphoniomethylidene complex [Mo(N-t-Bu)(CHPPh2Me)(OHMT)Cl(Bipy)]Cl. The Mo(N-t-Bu)(CHX)(OHIPT)Cl(PPh2Me) complexes (X = Cl, CF3) were confirmed to initiate the stereoselective cross-metathesis between (Z)-5-decene and (Z)-XCH═CHX.

This tutorial explores the major pathways of forming metal–carbon double bonds in high-oxidation-state alkylidene complexes that began with the alkylidene chemistry of tantalum complexes in the 1970s and continued with the organometallic chemistry of Mo, W, and Re and the development of homogeneous catalysts for the metathesis of olefins. It also explores recent findings in surface organometallic chemistry and discusses the link between molecularly defined and heterogeneous catalysts. Recent results suggest that heterogeneous olefin metathesis catalysts that are activated toward metathesis upon exposure to olefins produce a d0 alkylidene through formation of a metallacyclopentane ring at d2 metal sites followed by “a ring contraction” to a metallacyclobutane, a reaction that was first observed in tantalum chemistry.

Reactions between Mo(N-t-Bu)(2)(CH(2)-t-Bu)(2) or Mo(NAdamantyl)(2)(CH(2)CMe(2)Ph)(2) and 3 equiv of HCl in the presence of 1 equiv of PPh(2)Me yield Mo(NR)(CHR’)(PPh(2)Me)Cl(2) complexes, from which Mo(NR)(CHR’)(PPh(2)Me)(OAr)Cl complexes (OAr = a 2,6-terphenoxide) can be prepared. The Mo(NR)(CHR’)(PPh(2)Me)(OAr)Cl complexes were evaluated as cross-metathesis catalysts between cyclooctene and Z-1,2-dichloroethylene. The efficiencies of the test reaction for complexes in which OAr = OTPP, OHMT, OHIPT, or OHTBT (where OTPP is 2,3,5,6-tetraphenylphenoxide, OHMT is hexamethylterphenoxide, OHIPT is hexaisopropylterphenoxide, and OHTBT is hexa-t-butylterphenoxide) maximize when OAr is OHMT or OHIPT. Mo(N-t-Bu)(CH-t-Bu)(PPh(2)Me)Cl(2) is essentially inactive for the reaction between cyclooctene and Z-1,2-dichloroethylene. X-ray structural studies were carried out on Mo(NAd)(CHCMe(2)Ph)(PPh(2)Me)Cl(2), Mo(N-t-Bu)(CH-t-Bu)(PPh(2)Me)(OHMT)Cl, Mo(NAd)(CHCMe(2)Ph)(Cl)(OHTBT)(PMe(3)), and [Mo(NAd)(CHCMe(2)Ph)(PMe(3))(Cl)](2)(μ-O), the product of the reaction between Mo(NAd)(CHCMe(2)Ph)(Cl)(OHTBT)(PMe(3)) and 0.5 equiv of water.

In the interest of preparing molybdenum and tungsten alkylidene complexes for olefin metathesis that are longer-lived at high temperatures (∼150 °C or above), we synthesized complexes that contain a phenoxide ligand with a 2-pyridyl in one ortho position and a mesityl (Mes) or 2,4,6-i-Pr3C6H2 (Trip) in the other ortho position ([MesON]− or [TripON]−, respectively). The alkylidene (neophylidene) complexes that were prepared include W(O)(CHCMe2Ph)(Me2Pyr)(RON) (R = Mes or Trip), Mo(NC6F5)(CHCMe2Ph)(RON)Cl, Mo(N-2,6-Me2C6H3)(CHCMe2Ph)(RON)Cl, Mo(N-t-Bu)(CHCMe2Ph)(RON)Cl, and M(N-2,6-i-Pr2C6H3)(CHCMe2Ph)(TripON)(OTf) (M = Mo or W). The reaction between Mo(NAr)(CHCMe2Ph)(TripON)(OTf) and ethylene yielded an ethylene complex, Mo(NAr)(C2H4)(TripON)(OTf)(ether). All neophylidene complexes were essentially unreactive toward terminal olefins at 22 °C and showed modest homocoupling activity (at 80 or 100 °C) and alkane metathesis activity (at 150 and 200 °C). W(O)(CHCMe2Ph)(Me2Pyr)(MesON) also stereoselectively poly...

Molybdenum imido alkylidene and tungsten oxo alkylidene complexes that contain a tridentate “pincer” [ONO]2– ligand have been prepared and treated with ethylene to give unsubstituted metallacyclobutane complexes that have a 16e count. Both Mo and W metallacyclobutane complexes exchange C2D4 into the metallacyclobutane ring at 22 °C at a rate that is first order in metal and zero order in C2D4. These metallacycles lose ethylene at least 104–105 times slower than reported 14e unsubstituted Mo and W metallacyclobutane complexes that have been explored in the literature that have a TBP geometry with the metallacyclobutane ring bound in the equatorial positions. Our studies suggest that breaking up the metallacyclobutane ring in these 16e d0 Mo or W complexes is slow because a 14e TBP metallacyclobutane complex cannot be accessed readily.

Ring-opening metathesis polymerization (ROMP) is used to prepare trans-poly(A-alt-B) polymers from a 1:1 mixture of A and B where A is a cyclic olefin such as cyclooctene (A1) or cycloheptene (A2) and B is a large norbornadiene or norbornene derivative such as 2,3-dicarbomethoxy-7-isopropylidenenorbornadiene (B1) or dimethylspirobicyclo[2.2.1]hepta-2,5-diene-2,3-dicarboxylate-7,1′-cyclopropane (B2). The most successful initiators that were examined are of the type Mo(NR)(CHCMe2Ph)[OCMe(CF3)2]2 (R = 2,6-Me2C6H3 (1) or 2,6-i-Pr2C6H3 (2)). The trans configuration of the AB linkages is proposed to result from the steric demand of B. Both anti-MB and syn-MB alkylidenes are observed during the copolymerization, where B was last inserted into a Mo═C bond, although anti-MB dominates as the reaction proceeds. anti-MB is lower in energy than syn-MB, does not react readily with either A or B, and interconverts slowly with syn-MB through rotation about the Mo═C bond. Syn-MB does not readily react with B, but it does ...

A variety of molybdenum or tungsten complexes that contain a tert-butylimido ligand have been prepared. For example, the o-methoxybenzylidene complex W(N-t-Bu)(CH-o-MeOC6H4)(Cl)2(py) was prepared through addition of pyridinium chloride to W(N-t-Bu)2(CH2-o-MeOC6H4)2, while Mo(N-t-Bu)(CH-o-MeOC6H4)(ORF)2(t-BuNH2) complexes (ORF = OC6F5 or OC(CF3)3) were prepared through addition of two equivalents of RFOH to Mo(N-t-Bu)2(CH2-o-MeOC6H4)2. An X-ray crystallographic study of Mo(N-t-Bu)(CH-o-MeOC6H4)[OC(CF3)3]2(t-BuNH2) showed that the methoxy oxygen is bound to the metal and that two protons on the tert-butylamine ligand are only a short distance away from one of the CF3 groups on one of the perfluoro-tert-butoxide ligands (H···F = 2.456(17) and 2.467(17) A). Other synthesized tungsten tert-butylimido complexes include W(N-t-Bu)(CH-o-MeOC6H4)(pyr)2(2,2′-bipyridine) (pyr = pyrrolide), W(N-t-Bu)(CH-o-MeOC6H4)(pyr)(OHMT) (OHMT = O-2,6-(mesityl)2C6H3), W(N-t-Bu)(CH-t-Bu)(OHMT)(Cl)(py) (py = pyridine), W(N-t-Bu)(CH-...

Molybdenum and tungsten alkylidene complexes that contain the sterically demanding hexaisopropylterphenylimido ligand, N-2,6-(2,4,6-i-Pr3C6H2)2C6H3 (NHIPT), have been prepared from Mo(N-t-Bu)2Cl2(1,2-dimethoxyethane) or W(N-t-Bu)2Cl2(pyridine)2, employing tert-butylimido ligands as sacrificial proton acceptors. These complexes include M(NHIPT)(CH-t-Bu)Cl2 (M = Mo, W), Mo(NHIPT)(CH-t-Bu)(pyrrolide)2, and Mo(NHIPT)(CH-t-Bu)(pyrrolide)(OC6F5)(CH3CN). In all cases only anti alkylidene isomers are observed in solution, as a consequence of the steric demands of the NHIPT ligand. An X-ray structure of W(NHIPT)(CH-t-Bu)Cl2 showed it to be a monomer with a disordered alkylidene that is 86% in the anti configuration and 14% in the syn configuration.

We have employed 2,3-dicarbomethoxynorbornadiene (DCMNBD) as a monomer to explore new tungsten oxo alkylidene complexes as initiators for stereoregular ROMP (ring-opening metathesis polymerization). The initiators include MAP (monoaryloxide pyrrolide) oxo alkylidene complexes with the general formula W(O)(CHCMe2Ph)(Me2Pyr)(OAr) (Me2Pyr = 2,5-dimethylpyrrolide, OAr = an aryloxide) and W(O)(CHCMe2Ph)(OR)2 (OR = an aryloxide or OC(CF3)3), or PPh2Me or CH3CN adducts thereof. We have found that MAP initiators yield cis,syndiotactic-poly(DCMNBD) as a consequence of stereogenic metal control. In contrast, W(O)(CHCMe2Ph)(OR)2(L) initiators (where L = PPh2Me or acetonitrile) are strongly biased toward formation of cis,isotactic structures, while W(O)(CHCMe2Ph)(OR)2 initiators are strongly biased toward formation of cis,syndiotactic structures. Addition of B(C6F5)3 to W(O)(CHCMe2Ph)(Me2Pyr)(OR) species leads to a dramatic increase in the rate of polymerization and to an increase in the cis,syndiotacticity of the po...

Monoalkoxide pyrrolide (MAP) complexes that contain a 2,6-dimesitylphenylimido (NAr*) ligand react with ethylene to yield unsubstituted metallacyclobutanes that are in equilibrium with methylidene complexes, W(NAr*)(CH2)(Me2Pyr)(OR) (R = t-Bu, OCMe(CF3)2, SiPh3, or 2,6-Me2C6H3). Polymerization of 2,3-dicarbomethoxynorbornadiene (DCMNBD) with M═CHCMe2Ph (M = Mo or W) initiators is slow as a consequence of a slow propagation step. However, W(NAr*)(CH2)(Me2Pyr)(OR) (R = SiPh3 or 2,6-dimethylphenyl) complexes react readily with 1 equiv of DCMNBD to give a monoinsertion product. The facile reaction between the monoinsertion product and ethylene then allows these complexes to be catalyts for the ring-opening cross-metathesis (ethenolysis) of DCMNBD and DCMNBE (2,3-dicarbomethoxynorbornene) with minimal formation of polymer.

We have found that coordination of B(C6F5)3 to an oxo ligand in tungsten oxo alkylidene bis(aryloxide) complexes, where the aryloxide is O-2,6-(mesityl)2C6H3 (HMTO) or 2,6-diadamantyl-4-methylphenoxide (dAdPO), accelerates the formation of metallacyclobutane complexes from alkylidenes as well as the rearrangement of metallacyclobutane complexes. In contrast, a tungstacyclopentane complex, W(O)(C4H8)(OHMT)2, is relatively stable toward rearrangement in the presence of B(C6F5)3. A careful balance of steric factors allows a single isomer of W(O)(trans-4,4-dimethylpent-2-ene)(dAdPO)2 to be formed from W(O)(CH-t-Bu)(dAdPO)2 in the presence of both ethylene and B(C6F5)3.

Ring-opening metathesis polymerization of a series of 3-substituted cyclooctenes (3-MeCOE, 3-HexCOE, and 3-PhCOE) initiated by various Mo and W MAP complexes leads to cis,HT-poly(3-RCOE) polymers. The apparent rate of polymerization of 3-HexCOE by W(N-t-Bu)(CH-t-Bu)(Pyr)(OHMT) (1c; Pyr = pyrrolide; OHMT = O-2,6-Mesityl2C6H3) is greater than the rate of polymerization by Mo(N-t-Bu)(CH-t-Bu)(Pyr)(OHMT) (1b), but both gave the same cis,HT polymer structures. Formation of HT-poly(3-RCOE) employing 1c takes place via propagating species in which the R group (methyl, hexyl, or phenyl) is on C2 of the propagating alkylidene chain, a type of intermediate that has been modeled through the preparation of W(N-t-Bu)(CHCHMeEt)(Pyr)(OHMT). The rate of ROMP is exceedingly sensitive to steric factors: e.g., W(N-t-Bu)(CH-t-Bu)(Me2Pyr)(OHMT), the dimethylpyrrolide analogue of 1c, essentially did not polymerize 3-HexCOE at 22 °C. When a sample of W(N-t-Bu)(CHCHMeEt)(Pyr)(OHMT) and 3-methyl-1-pentene in CDCl3 is cooled to −2...

Reactions between Mo(NAr)(CHR)(Me2Pyr)-(OTPP) (Ar = 2,6-i-Pr2C6H3, R = H or CHCMe2Ph, Me2Pyr = 2,5-dimethylpyrrolide, OTPP = O-2,3,5,6-Ph4C6H) and CH2=CHX where X = B(pin), SiMe3, N-carbazolyl, N-pyrrolidinonyl, PPh2, OPr, or SPh lead to Mo(NAr)(CHX)-(Me2Pyr)(OTPP) complexes in good yield. All have been characterized through X-ray studies (as an acetonitrile adduct in the case of X = PPh2). The efficiencies of metathesis reactions initiated by Mo(NAr)(CHX)(Me2Pyr)(OTPP) complexes can be rationalized on the basis of steric factors; electronic differences imposed as a consequence of X being bound to the alkylidene carbon do not seem to play a major role. Side reactions that promote catalyst decomposition do not appear to be a serious limitation for Mo=CHX species.

The bisDFTO alkylidene complexes of molybdenum Mo(NR)(CHCMe2Ph)(DFTO)2 (R = 2,6-i-Pr2C6H3, 2,6-Me2C6H3, C6F5, 1-adamantyl; DFTO = 2,6-(C6F5)2C6H3O) and monoaryloxide monopyrrolide (MAP) complexes Mo(NR)(CHCMe2Ph)(Me2Pyr)(OAr) (Me2Pyr = 2,5-dimethylpyrrolide; R = C6F5, OAr = DFTO, 2,6-dimesitylphenoxide (HMTO); R = 2,6-Me2C6H3, OAr = DFTO) have been prepared in good yields. Addition of dicarbomethoxynorbornadiene (DCMNBD) to bisDFTO complexes yielded polymers that have a cis,isotactic structure. Polymerization of DCMNBD by Mo(NC6F5)(CHCMe2Ph)(Me2Pyr)(HMTO) gives a polymer that contains the expected cis,syndiotactic structure, but polymerization of DCMNBD by Mo(NR)(CHCMe2Ph)(Me2Pyr)(DFTO) (R = C6F5, 2,6-Me2C6H3) generates a polymer that has a cis,isotactic structure, the first observation of a cis,isotactic polymer prepared employing a MAP initiator. Norbornene is polymerized to give what is proposed to be highly tactic cis-polyNBE. Addition of ethylene to Mo(NC6F5)(CHCMe2Ph)(DFTO)2 leads to formation of Mo...

Molybdenum and tungsten bispyrrolide alkylidene complexes that contain a 2,6-dimesitylphenylimido (NAr*) ligand have been prepared, in which the pyrrolide is the parent pyrrolide or 2,5-dimethylpyr...

Reaction of W(O)2(CH2-t-Bu)2(bipy) with a mixture of ZnCl2(dioxane), PMe2Ph, and trimethylsilyl chloride in toluene at 100 °C produced the known tungsten oxo alkylidene complex W(O)(CH-t-Bu)Cl2(PMe2Ph)2 (1a) in 45% isolated yield. The neophylidene analogue W(O)(CHCMe2Ph)Cl2(PMe2Ph)2 was prepared similarly in 39% yield. The reaction between 1a and LiOR (LiOR = LiOHIPT, LiOHMT) in benzene at 22 °C led to formation of the off-white W(O)(CH-t-Bu)Cl(OR)(PMe2Ph) complexes 4a (OR = OHMT = 2,6-dimesitylphenoxide) and 4b (OR = OHIPT = 2,6-(2,4,6-triisopropylphenyl)2phenoxide). Compound 4a serves as a starting material for the synthesis of W(O)(CH-t-Bu)(OHMT)(2,6-diphenylpyrrolide) (6), W(O)(CH-t-Bu)[N(C6F5)2](OHMT)(PMe2Ph) (7), W(O)(CH-t-Bu)[OSi(t-Bu)3](OHMT) (8), and W(O)(CH-t-Bu)(OHMT)2 (10). The reaction between 8 and ethylene was found to yield the square-pyramidal metallacyclobutane complex W(O)(C3H6)[OSi(t-Bu)3](OHMT) (9), while the reaction between 10 and ethylene was found to yield the square-pyramidal met...

Routes to new tungsten alkylidene complexes that contain tert-butylimido or adamantylimido ligands have been devised that begin with a reaction between WCl6 and 4 equivalents of HNR(TMS) to give [W(NR)2Cl(μ-Cl)(RNH2)]2 (R = t-Bu or 1-adamantyl). Alkylation leads to W(NR)2(CH2R′)2 (R′ = t-Bu or CMe2Ph), which upon treatment with pyridinium chloride yields W(NR)(CHR′)Cl2(py)2 complexes, from which W(NR)(CHR′)(pyrrolide)2 and two W(N-t-Bu)(CHR′)(pyrrolide)(OAr) complexes (OAr = hexamethyl- or hexaisopropylterphenoxide) have been prepared.

In this paper we describe the syntheses of several new stereogenic-at-metal imido alkylidene complexes of molybdenum, Mo(NR)(CHR′)(X)(Y), many of which had to be prepared through selective nucleophilic displacement reactions in imido alkylidene complexes. The reported compounds include Mo(NAd)(CHCMe2Ph)(MesPyr)2 (1a; MesPyr = 2-mesitylpyrrolide, Ad = 1-adamantyl), Mo(NAd)(CHCMe2Ph)(2-CNPyr)2 (1b; 2-CNPyr = 2-cyanopyrrolide), Mo(NAd)(CHCMe2Ph)(MesPyr)(OTPP) (2a; OTPP = 2,3,5,6-tetraphenylphenoxide), Mo(NAd)(CHCMe2Ph)(MesPyr)(OBr2Bitet) (2b; OBr2Bitet = (R)-3,3′-dibromo-2′-(tert-butyldimethylsilyloxy)-5,5′,6,6′,7,7′,8,8′-octahydro-1,1′-binaphthyl-2-olate), Mo(NAd)(CHCMe2Ph)(OHIPT)(2-Mespyr) (2c; HIPT = 2,6-(2,4,6-iPr3C6H2)2C6H3), Mo(NAd)(CHCMe2Ph)(OTf)(OHIPT) (3), Mo(NAd)(CHCMe2Ph)(OTf)(OHIPT)(PMe3) (3(PMe3)), Mo(NAd)(CHCMe2Ph)(2-CNPyr)(OHIPT) (4), Mo(NAd)(CHCMe2Ph)(OHIPT)(OCMe3) (5), Mo(NR)(CHCMe2Ph)(ORF6)(OHMT) (ORF6 = OCMe(CF3)2; HMT = 2,6-Mes2C6H3; R = 2,6-iPr2C6H3 (Ar, 6a), 2,6-Me2C6H3 (Ar′, 6b), 2-iPr...

Pentafluorophenylimido alkylidene complexes of molybdenum and tungsten have been prepared in good yields. Examples include Mo(NC6F5)(CHCMe2Ph)(Me2Pyr)2 (Me2Pyr = 2,5-dimethylpyrrolide), W(NC6F5)(CH-t-Bu)(DME)(Pyrrolide)2, Mo(NC6F5)(CHCMe2Ph)[OC(CF3)3]2, W(NC6F5)(CH-t-Bu)(DME)[OC(CF3)3]2, Mo(NC6F5)(CHCMe2Ph)[OC(C6F5)3]2, W(NC6F5)(CH-t-Bu)[OC(C6F5)3]2, Mo(NC6F5)(CHCMe2Ph)(ODFT)2 (ODFT = O-2,6-(C6F5)2C6H3), and W(NC6F5)(CH-t-Bu)(ODFT)2. Treatment of W(NC6F5)(CH-t-Bu)(DME)[OC(CF3)3]2 with ethylene led to formation of W(NC6F5)(CH2CH2CH2)[OC(CF3)3]2, which has a TBP structure in which the metallacyclobutane ring lies in the equatorial plane. 2,3-Dicarbomethoxynorbornadiene is polymerized by M(NC6F5)(CHR′)(ODFT)2 initiators to give cis,isotactic-poly(DCMNBD).

Monaryloxide pyrrolide (MAP) molybdenum imido alkylidene complexes of the type Mo(NArX)(CHCMe2R)(Me2Pyr)(OR′) (Me2Pyr = 2,5-dimethylpyrrolide) have been prepared in which NArX is an ortho-substituted phenylimido group (X = Cl (NArCl), CF3 (NArCF3), i-Pr (NAriPr), t-Bu (NArtBu), mesityl (NArM), or TRIP (TRIP = triisopropylphenyl; NArT)) and OR′ = O-2,3,5,6-(C6H5)4C6H (OTPP), O-2,6-(2,4,6-Me3C6H2)2C6H3 (OHMT), or O-2,6-(2,4,6-i-Pr3C6H2)2C6H3 (OHIPT). The object was to explore to what extent relatively “large” NArM or NArT ligands would alter the performance of MAP catalysts in reactions that have been proposed to depend upon the relative size of the imido and OR′ groups. Preliminary studies employing the ring-opening metathesis polymerization of 5,6-dicarbomethoxynorbornadiene as a measure of selectivity suggest that a single phenylimido ortho substituent, even in an NArM or NArT group, does not produce any unique behavior and that the outcome of the ROMP reaction correlates with the overall relative size o...

Exposure of heptane solutions of Mo(NAr)(CHCMe2Ph)(Me2Pyr)(OAr) (1a; Ar = 2,6-diisopropylphenyl), Mo(NAr)(CHCMe3)(Me2Pyr)[OCMe(CF3)2] (1b), and Mo(NAr)(CHCMe2Ph)(Me2Pyr)(OSiPh3) (1c) to one atmosphere of ethylene for 12 h yields the ethylene complexes, Mo(NAr)(CH2CH2)(Me2Pyr)(OAr) (2a), Mo(NAr)(CH2CH2)(Me2Pyr)[OCMe(CF3)2] (2b), and Mo(NAr)(CH2CH2)(Me2Pyr)(OSiPh3) (2c). Addition of 1 equiv of triphenylsilanol to a solution of 2c gives Mo(NAr)(CH2CH2)(OSiPh3)2 (3) readily. Mo(NAr)(CHCMe2Ph)(OTf)2(dme) reacts slowly with ethylene (60 psi) in toluene at 80 °C to give cis and trans isomers of Mo(NAr)(CH2CH2)(OTf)2(dme) (4a) in the ratio of ∼2(cis):1. Addition of lithium 2,5-dimethylpyrrolide to 4a under 1 atm of ethylene produces Mo(NAr)(CH2CH2)(η1-Me2Pyr)(η5-Me2Pyr) (5a). Mo(NAr)(CHCMe2Ph)(η1-MesPyr)2 (MesPyr = 2-mesitylpyrrolide) reacts cleanly with ethylene in benzene at 60 °C over a period of four days to give exclusively Mo(NAr)(CH2CH2)(MesPyr)2 (5b). Treatment of 5b with 2 equiv of (CF3)2CHOH in ether yi...

Addition of ethylene to Mo(NAr)(CHCMe2Ph)(OHIPT)(Pyr) (NAr = N-2,6-i-Pr2C6H3, OHIPT = O-2,6-(2,4,6-i-Pr3C6H2)2C6H3, Pyr = NC4H4) led to the trigonal-bipyramidal metallacyclobutane complex Mo(NAr)(C...

Over 40 molybdenum and tungsten imido alkylidene mono(alkoxide) mono(pyrrolide) (MAP) or bis(alkoxide) olefin metathesis catalysts were examined in combination with Ir-based pincer-type catalysts for the metathesis of n-octane. The imido group, alkoxide, and metal in the metathesis catalysts were all found to be important variables. The best catalyst was W(NAr)(CHR)(OSiPh3)2 (Ar = 2,6-diisopropylphenyl), which performed about twice as well as the only previously employed catalyst, Mo(NAr)(CHR)[OCMe(CF3)2]2. Product yields decreased at temperatures greater than 125 °C, most likely because of the instability of the metathesis catalysts at such temperatures. POCOP Ir catalysts gave higher yields than PCP Ir catalysts, although the latter exhibited some selectivity for formation of tetradecane. Eight catalysts were synthesized in situ through addition of alcohols to bis(2,5-dimethylpyrrolide) complexes; in situ catalysts were shown to perform approximately as well as the isolated complexes, which suggests tha...

An X-ray structural study of Mo(NAd)(CHCMe2Ph)(2,5-Me2NC4H2)2 (1; Ad = 1-adamantyl) reveals it to contain one η1-2,5-Me2NC4H2 ring and one η5-2,5-Me2NC4H2 ring. The structures of Mo(NAr)(CHCMe2Ph)(...

In this paper we demonstrate a method of synthesizing oligoenes of diisopropyldipropargylmalonate, [CH2][bx][CH2] (x = 2, 3, 4, 5), in which the “b” repeat unit is identical to the five-membered ring formed in a tail-to-tail cyclopolymerization of diisopropyldipropargylmalonate, and methylene groups are capping the ends. For example, a “degenerate” metathesis reaction between the “monomer”, [CH2][b][CH2], and 2 equiv of Mo(NAr′)(CHCMe2Ph)(ORF6)2 ([Mo][CHCMe2Ph] where Ar′ = 2,6-Me2C6H3 and ORF6 = OCMe(CF3)2) gives [Mo][b][Mo]. An “Mo-Wittig” reaction between [Mo][b][Mo] and 2 equiv of the aldehyde, [CH2][b][O], then gives the “trimer”, [CH2][b3][CH2]. Treatment of [CH2][b3][CH2] with 2 equiv of [Mo][CHCMe2Ph] gives [Mo][b3][Mo], which upon treatment with 2 equiv of [CH2][b][O] gives the “pentamer”, [CH2][b5][CH2], which contains 11 double bonds in conjugation in a molecule in which the repeat units are connected by trans C═C bonds. The oligoenes are not always obtained in high yield in pure form because (i...

Addition of 1 equiv of [HNMe2Ph]BArF4 (ArF = 3,5-(CF3)2C6H3) to Mo(NAr)(CHCMe2Ph)(Pyrrolide)2 (Pyrrolide = parent pyrrolide (Pyr) or 2,5-dimethylpyrrolide (Me2Pyr)) species in THF produced [Mo(NAr)(CHCMe2Ph)(Pyrrolide)(THF)x]BArF4 species (x = 2 for Me2Pyr (1b) or 3 (1a) for Pyr; Ar = 2,6-diisopropylphenyl). [Mo(NAr)(CHCMe2Ph)(Me2Pyr)(2,4-lutidine)]BArF4 (1c) was formed upon addition of 2,4-lutidine to [Mo(NAr)(CHCMe2Ph)(Me2Pyr)(THF)2]BArF4 (1b). Addition of 1 equiv of hexafluoro-tert-butanol to 1a produced {Mo(NAr)(CHCMe2Ph)[OC(CF3)2Me](THF)3}BArF4 (3a), while {Mo(NAr)(CHCMe2Ph)[OCMe(CF3)2](THF)2}BArF4 (3b) was obtained similarly through addition of hexafluoro-tert-butanol to 1b. Similar reactions produced unstable [Mo(NAr)(CHCMe2Ph)(O-2,6-i-Pr2C6H3)(THF)]BArF4 (3c) and [Mo(NAr)(CHCMe2Ph)(OAdamantyl)(THF)2]BArF4 (3d). Treatment of 1b with 2 equiv of 2,6-diisopropylphenol yielded [Mo(NAr)(CH2CMe2Ph)(O-2,6-i-Pr2C6H3)2]BArF4 (4). Compound 3a reacts with ethylene to yield {Mo(NAr)(CH2CH2)[OC(CF3)2Me](THF)3}B...

The carboxylate species Mo(NR)(CHCMe2R′)(O2CCPh3)2 (R = various aryl groups or 1-adamantyl; R′ = Ph or Me) have been synthesized by salt metathesis between Mo(NR)(CHCMe2R′)(OTf)2(DME) (OTf = trifluoromethanesulfonate; DME = 1,2-dimethoxyethane) and sodium triphenylacetate. Other carboxylate compounds that have been prepared by this route include Mo(NAr)(CHCMe2Ph)(O2CR′′)2 (Ar = 2,6-i-Pr2C6H3; R′′ = CPh2Me, Si(SiMe3)3) and Na[Mo(NAd)(CHCMe2Ph)(O2CAr′)3] (Ar′ = 2,6-Me2C6H3). Terphenylcarboxylate species Mo(NR)(CHCMe2Ph)(O2CTer)2 (Ter = 2,6-diphenyl-4-methylphenyl or 2,6-diphenyl-4-methoxyphenyl) were prepared through protonolysis of Mo(NR)(CHCMe2R′)(Me2Pyr)2 with TerCO2H, and one of them was characterized through X-ray crystallography. Trimethylphosphine adducts of selected triphenylacetate complexes have been isolated, and the X-ray crystal structure of Mo(NAr′′)(CH-t-Bu)(O2CCPh3)2(PMe3) (Ar′′ = 2-t-BuC6H4) was obtained. Several of the triphenylacetate complexes are active initiators for the regioselective...

(Me2CF3CO)2(Ar′N)W═W(NAr′)(OCMe2CF3)2 (Ar′ = 2,6-Me2C6H3) reacts immediately at room temperature with 1 equiv of CCl4 to give the sparingly soluble [W(OCMe2CF3)2Cl]2(μ-NAr′)2. [W(NAr′)(OCMe2CF3)2]2 forms 1:1 adducts with simple donor ligands such as PMe3, PPhMe2, and pyridine, in which the base is likely to be coordinated to a single W center. Addition of ethylene to [W(NAr′)(OCMe2CF3)2]2 yields [W(NAr′)(OCMe2CF3)2]2(μ-C2H4), in which ethylene is bound essentially to one W, although it also could be argued that a 1,2-dimetallacyclobutane ring is present. Heating a toluene solution of [W(NAr′)(OCMe2CF3)2]2(μ-C2H4) produces (OCMe2CF3)2(Et)W(μ-NAr′)(μ-N-2-CH2-6-MeC6H3)W(OCMe2CF3)2, in which the proton required to form the ethyl ligand arises through CH activation in one of the methyl groups of the NAr′ ligand. Treatment of [W(NAr′)(OCMe2CF3)2]2 with 2-butyne yields [W(NAr′)(OCMe2CF3)2]2(μ-MeCCMe). Addition of 4 equiv of CH3CN to [W(NAr′)(OCMe2CF3)2]2 in benzene gives a mixture of two products, A and B, which...

Monosiloxide and disiloxide complexes have been prepared through the addition of silanols to Mo(NR)(CHCMe2Ph)(pyrrolyl)2 species [R = 1-adamantyl (Ad) or 2,6-i-Pr2C6H3 (Ar)]. The silanols employed ...

We have prepared tungsten bispyrrolyl (Pyr) or bis-2,5-dimethylpyrrolyl (Me2Pyr) complexes W(NAr)(CHCMe2Ph)(η1-Pyr)2(DME) (1), W(NAr)(CHCMe2Ph)(η1-Me2Pyr)(η5-Me2Pyr) (2), W(NArCl)(CHCMe3)(η1-Pyr)2(DME) (3b), and W(NArCl)(CHCMe3)(η1-Me2Pyr)(η5-Me2Pyr) (4) (Ar = 2,6-diisopropylphenyl, ArCl = 2,6-dichlorophenyl) in excellent yields by treating the appropriate W(NR)(CHCMe2R‘)(OTf)2(DME) species with LiPyr or LiMe2Pyr. Compounds 2 and 4 react with ethylene slowly to yield stable methylene complexes, W(NAr)(CH2)(η1-Me2Pyr)(η5-Me2Pyr) (5) and W(NArCl)(CH2)(η1-Me2Pyr)(η5-Me2Pyr) (6). In contrast, treatment of what is believed to be a fortuitous 1:1 mixture of 3b and [W(NArCl)(CHCMe3)(η1-Pyr)2][W(NArCl)(CHCMe3)(η1-Pyr)(η5-Pyr)] with ethylene leads to formation of [W(μ-NArCl)(η1-Pyr)2]2 (7) in moderate (54%) yield. Compounds 2 and 4 react with [HNMe2Ph][B(ArF)4] (ArF = 3,5-(CF3)2C6H3) in dichloromethane to yield cationic species that contain one η5-Me2Pyr ligand and one 2,5-dimethylpyrrolenine ligand formed through...

The molybdenum β-diketiminate complexes Mo(NR)(CHCMe2R‘)(Ar-nacnac)(OTf) (R = 2,6-diisopropylphenyl, 2,6-dimethylphenyl, 1-adamantyl, 2,6-dichlorophenyl, or 2-tert-butylphenyl; Ar = 2,6-dichlorophenyl, 2,6-dimethylphenyl, 3,5-dimethylphenyl, or 2,6-difluorophenyl; R‘ = Me or Ph; Ar-nacnac = [ArNC(Me)]2CH; OTf = trifluoromethanesulfonate) have been prepared from Mo(NR)(CHCMe2R‘)(OTf)2(DME) by metathesis with the corresponding Li{Ar-nacnac} salt. Reaction of Mo(NR)(CHCMe2R‘)(Ar-nacnac)(OTf) with NaBArf4 (Arf = 3,5-(CF3)2C6H3) in the presence or absence of THF affords the cationic species {Mo(NR)(CHCMe2R‘)(Ar-nacnac)(THF)n}{BArf4} (n = 0 or 1) depending on the nature of Ar. The reactivity of the cationic β-diketiminate (nacnac) complexes toward olefins has been examined, as has the thermal decomposition modes of the neutral and cationic nacnac complexes. Results demonstrate that the cationic species have short catalyst lifetimes and that decomposition modes dominate the chemistry of several of the nacnac com...

Tungsten alkylidene complexes that contain the 2,6-dichlorophenylimido ligand (NArCl), W(NArCl)(CHCMe3)(ORF6)2 and W(NArCl)(CHCMe3)(Biphen)(THP) (ORF6 = OCMe(CF3)2; Biphen2- = 3,3‘-di-t-Bu-5,5‘,6,6‘-tetramethyl-1,1‘-biphenyl-2,2‘-diolate; THP = tetrahydropyran), have been prepared from W(NArCl)(CHCMe3)(OSO2CF3)2(dme). Reaction of W(NArCl)(CHCMe3)(ORF6)2 with excess ethylene gave the tungstacyclobutane complex W(NArCl)(ORF6)2(C3H6), while reaction of W(NArCl)(CHCMe3)(ORF6)2 with internal olefins gave the dimer, [W(μ-NArCl)(ORF6)2]2. W(NArCl)(CHCMe3)(Biphen)(THP) reacted with excess ethylene to give W(NArCl)(Biphen)(C3H6), which yielded W(NArCl)(Biphen)(C2H4)(THF) upon addition of THF. The tungstacyclopentane complex, W(NArCl)(Biphen)(C4H8), was formed upon treatment of W(NArCl)(Biphen)(C2H4)(THF) with ethylene. W(NArCl)(Biphen)(C3H6) decomposed to yield (inter alia) the dimeric, heterochiral methylidene complex, [W(NArCl)(Biphen)(μ-CH2)]2, which decomposed further to yield homochiral [W(NArCl)(Biphen)]2(μ-...

Molybdenum olefin metathesis catalysts that contain aliphatic 1-phenylcyclohexylimido (NPhCy) and 2-phenyl-2-adamantylimido (NPhAd) groups and (S)-Biphen or (R)-Trip)(THF) ligands (Biphen = 3,3'-di-tert-butyl-5,5',6,6'-tetramethyl-1,1'-biphenyl-2,2'-diolate; Trip = 3,3'-bis(2,4,6-triisopropylphenyl)-2,2'-binaphtholate) have been prepared. Their catalytic activity and enantioselectivity in desymmetrization reactions such as ring-closing metathesis of amines and lactams and ring-opening/cross-metathesis of substituted norborneols with styrene were compared to the results obtained with the only known alkylimido catalyst Mo(NAd)(CHCMe(2)Ph)[(S)-Biphen]. The activities and enantioselectivities provided by these new chiral complexes vary significantly, but in virtually all instances explored were not superior to the adamantylimido analogs.

We have found that Mo(NAr)(CHR')(NPh(2))(2) (R' = t-Bu or CMe(2)Ph) and Mo(NAr')(CHCMe(2)Ph)(NPh(2))(2) (Ar = 2,6-i-Pr(2)C(6)H(3); Ar' = 2,6-Me(2)C(6)H(3)) can be prepared through addition of two equivalents of LiNPh(2) to Mo(NR″)(CHR')(OTf)(2)(dme) species (R″ = Ar or Ar' dme = 1,2-dimethoxyethane), although yields are low. A high yield route consists of addition of LiNPh(2) to bishexafluro-t-butoxide species. An X-ray structure of Mo(NAr)(CHCMe(2)Ph)(NPh(2))(2) reveals that the two diphenylamido groups are oriented in a manner that allows an 18 electron count to be achieved. The diphenylamido complexes react readily with t-BuOH and (CF(3))(2)MeCOH, but not readily with the sterically demanding biphenol H(2)[Biphen] (Biphen(2-) = 3,3'-Di-t-butyl-5,5',6,6'-tetramethyl-1,1'-Biphenyl-2,2'-diolate). The diphenylamido complexes do react with various 3,3'-disubstituted binaphthols to yield binaphtholate catalysts that can be prepared in situ and employed for a simple asymmetric ring-closing metathesis reaction. In several cases conversions and enantioselectivities were comparable to reactions in which isolated catalysts were employed.

The reaction of Ph3PCH2 with Mo(NAr)(CHCMe3)[OCMe(CF3)2]2 (Ar = 2,6-i-Pr2C6H3) produces the anionic alkylidyne complex {Ph3PMe}{Mo(NAr)(CCMe3)[OCMe(CF3)2]2}. An X-ray structure determination of the complex reveals a bent Mo−N−C angle for the imido group, as expected when a metal−carbon triple bond is present. The anion has been shown to react with electrophiles predominantly at the imido nitrogen.

The reaction between Mo(NAr)(trans-CHCHCHMe)[OCMe(CF3)2]2(quin) (Ar = 2,6-i-Pr2-C6H3; quin = quinuclidine) and lithium tert-butoxide yields Mo(NAr)(trans-CHCHCHMe)(O-t-Bu)2(quin) (1). The achiral,s...

Compounds that contain an unbridged WW bond can be prepared through bimolecular decomposition of various imido alkylidene complexes. One type of WW species is [W(NR)(CH2-t-Bu)(OR‘)]2 (R = 2,6-dimethylphenyl (Ar‘) or 2,6-diisopropylphenyl (Ar); R‘ = pentafluorophenyl or hexafluoroisopropyl), which is found in both heterochiral and homochiral forms. The other type is [W(NR)(OR‘)2]2 (R‘ = trifluoro-tert-butyl or hexafluoro-tert-butyl). All species contain an unbridged W(IV)/W(IV) double bond with a WW bond distance of 2.4−2.5 A, a 90° angle between the imido ligands and the WW bond, and an anti relationship of the imido ligands. There is no indication that WW bonds are broken spontaneously; for example, heterochiral and homochiral [W(NR)(CH2-t-Bu)(OR‘)]2 species do not interconvert.

The reaction between M(NAr)(CH-t-Bu)(CH2-t-Bu)2 (M = Mo, W, Ar = 2,6-i-Pr2C6H3) and various alcohols (1-adamantyl-OH, t-BuOH, ArOH, (CF3)2CHOH, (CF3)2MeCOH, CF3Me2COH, (CF3)3COH, C6F5OH) in pentane...

An X-ray study of [(THF)(RF6O)2(ArN)MoCH]2(1,4-C6H4) (ORF6 = OCMe(CF3)2; Ar = 2,6-diisopropylphenyl; THF = tetrahydrofuran; 1b), which is closely related to known [(DME)(RF6O)2(ArN)MoCH]2(1,4-C6H4) (DME = 1,2-dimethoxyethane; 1a), showed it to be the expected bimetallic species in which each end is approximately a trigonal bipyramidal monoadduct of a syn alkylidene with the THF coordinated to the NOO face of the metal trans to the MoC bond. Treatment of 1a with lithium tert-butoxide yielded [(t-BuO)2(ArN)MoCH]2(1,4-C6H4) (2). Addition of divinylferrocene to Mo(CHCMe2Ph)(NAr)(ORF6)2 produced the bimetallic species {(RF6O)2(ArN)Mo[CH(C5H4)]}2Fe (3), which upon treatment with lithium tert-butoxide produced a related tert-butoxide complex (4). X-ray studies of 3 and 4 showed them to be “syn/syn” bimetallic species related to 1b. In solution two resonances can be observed in proton NMR spectra in the alkylidene region for the “syn/anti” isomer of 1a, 2, 3, and 4; the total amount varies between 4 and 20% of th...

Reactions between [HIPTN3N]Mo(N2) and ethylene, acetylene, or CO yield Mo(η2-C2H4), Mo(η2-C2H2), and Mo(CO), respectively ([HIPTN3N]3- = [3,5-(2,4,6-i-Pr3C6H2)2C6H3NCH2CH2]3N3-; HIPT = hexaisopropylterphenyl; [HIPTN3N]Mo = Mo). All are paramagnetic C3 symmetric species. Attempts to prepare Mo(CO) through reduction of MoCl with Na/Hg in THF under carbon monoxide yielded [Mo(CO)]Na, in which the sodium ion is believed to be bound within the HIPT aryl system. Addition of a variety of acids such as [Et3NH]BAr‘4 to [Mo(CO)]Na led to formation of the carbonyl hydride, Mo(CO)H, which also could be prepared by treating MoH with CO. Reactions between MoH and ethylene, 1-hexene, or 1-octene in benzene yield paramagnetic, red Mo(CH2R) complexes (CH2R = ethyl, hexyl, or octyl). MoMe could be prepared by treating MoCl with AlMe3 at room temperature over a period of 2 days. Treatment of MoH with acetylene affords yellow diamagnetic Mo(η2-CHCH2) plus polyacetylene. The MoCH2R complexes decompose at ∼150 °C to yield the ...

The diamine rac-H2[MepyN] (rac-N,N‘-di(6-methylpyridin-2-yl)-2,2‘-diaminobinaphthalene) has been prepared in good yield through reductive amination of rac-2,2‘-diaminobinaphthalene with 6-methylpyridinecarboxaldehyde. The [MepyN]2- ligand has been employed to prepare a variety of zirconium and hafnium complexes, [MepyN]MX2 (M = Zr, X = NMe2, Cl, OSO2CF3, CH2CHMe2, CH2Ph; M = Hf, X = NMe2, OSO2CF3, CH2CHMe2). The solid state structures of [MepyN]Zr(CH2Ph)2, [MepyN]Zr(NMe2)Cl, [MepyN]Hf(CH2CHMe2)2, and [MepyN]Hf(OSO2CF3)2 have been determined by X-ray diffraction. Activation of [MepyN]Zr(CH2Ph)2 and [MepyN]Hf(CH2CHMe2)2 with various Lewis acids leads to observable cationic alkyls that are not active toward 1-hexene polymerization.