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A varietyof 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= OC6F5or OC(CF3)3) were prepared through addition of two equivalentsof 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 twoprotons on the tert-butylamine ligand are only ashort distance away from one of the CF3groups on one ofthe perfluoro-tert-butoxide ligands (H···F= 2.456(17) and 2.467(17) Å). 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-t-Bu)(OHMT)(Cl), W(N-t-Bu)(CH-t-Bu)(pyr)(ODFT)(py), W(N-t-Bu)(CH-t-Bu)(OHMT)2, and W(N-t-Bu)(CH-t-Bu)(ODFT)2(ODFT = O-2,6-(C6F5)2C6H3). Interestingly, W(N-t-Bu)(CH-t-Bu)(OHMT)2does not react with ethylene or 2,3-dicarbomethoxynorbornadiene.Removal of pyridine from W(N-t-Bu)(CH-t-Bu)(BiphenCF3)(pyridine) (BiphenCF3= 3,3′-di-tert-butyl-5,5′-bistrifluoromethyl-6,6′-dimethyl-1,1′-biphenyl-2,2′-diolate)with B(C6F5)3led to formation ofa five-coordinate 14eneopentyl complex as a consequenceof CH activation in one of the methyl groups in one tert-butyl group of the BiphenCF3ligand, as was proven inan X-ray study. An attempted synthesis of W(N-t-Bu)(CH-t-Bu)(BiphenMe) (BiphenMe=3,3′-di-tert-butyl-5,5′,6,6′-tetramethyl-1,1′-biphenyl-2,2′-diolate)led to formation of a 1:1 mixture of W(N-t-Bu)(CH-t-Bu)(BiphenMe) and a neopentyl complexanalogous to the one characterized through an X-ray study. The metallacyclobutanecomplexes W(N-t-Bu)(C3H6)(pyrrolide)(ODFT)and W(N-t-Bu)(C3H6)(ODFT)2were prepared in reactions involving W(N-t-Bu)(CH-t-Bu)(pyr)2(bipy), ZnCl2(dioxane), and one or two equivalents of DFTOH, respectively,under 1 atm of ethylene. [ABSTRACT FROM AUTHOR]

Molybdenumand tungsten alkylidene complexes that contain the stericallydemanding hexaisopropylterphenylimido ligand, N-2,6-(2,4,6-i-Pr3C6H2)2C6H3(NHIPT), have been prepared from Mo(N-t-Bu)2Cl2(1,2-dimethoxyethane) orW(N-t-Bu)2Cl2(pyridine)2, employing tert-butylimido ligands as sacrificialproton 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 alkylideneisomers are observed in solution, as a consequence of the steric demandsof the NHIPT ligand. An X-ray structure of W(NHIPT)(CH-t-Bu)Cl2showed it to be a monomer with a disordered alkylidenethat is 86% in the anti configuration and 14% in the syn configuration. [ABSTRACT FROM AUTHOR]

Molybdenum and tungsten bispyrrolidealkylidene complexes thatcontain a 2,6-dimesitylphenylimido (NAr*) ligand have been prepared,in which the pyrrolide is the parent pyrrolide or 2,5-dimethylpyrrolide.Monoalkoxide pyrrolide (MAP) complexes were prepared through additionof 1 equiv of an alcohol to the bispyrrolide complexes. MAP compoundsthat contain the parent pyrrolide (NC4H4–) are pyridine adducts, while those that contain 2,5-dimethylpyrrolideare pyridine free. Molybdenum and tungsten MAP 2,5-dimethylpyrrolidecomplexes that contain O-t-Bu, OCMe(CF3)2, orO-2,6-Me2C6H3ligands were foundto have approximately equal amounts of synand antialkylidene isomers, which allowed a study of the interconversionof the two employing 1H–1H EXSY methods.The Keqvalues ([syn]/[anti]) are all 2–3 orders of magnitude smaller thanthose observed for a large number of Mo bisalkoxide imido alkylidenecomplexes, as a consequence of the destabilization of the synisomer by the sterically demanding NAr* ligand. Therates of interconversion of synand antiisomers were found to be 1–2 orders of magnitude faster forW MAP complexes than for Mo MAP complexes. [ABSTRACT FROM AUTHOR]

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 that 2,5-dimethylpyrrole is not detrimental to the alkane metathesis process and that potential catalysts can be screened more conveniently in this way. [ABSTRACT FROM AUTHOR]

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-Me2C6H3and 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 transCC bonds. The oligoenes are not always obtained in high yield in pure form because (inter alia) CC metathesis reactions compete with the Mo-Wittig reaction of the aldehyde (e.g., to give [CH2][b2][CH2] also in the synthesis of [CH2][b3][CH2]). These complications could be minimized by employing adducts (L)[Mo][bx][Mo](L), where L = PMe3or quinuclidine, instead of base-free [Mo][bx][Mo] species in the Mo-Wittig reaction. X-ray structures are reported for [CH2][b2][CH2], [CH2][b3][CH2], (THF)[Mo][b2][Mo](THF), (Et2O)[Mo][b3][Mo](Et2O), and a mixture of homochiral and heterochiral [quin][Mo][b][Mo][quin]. [ABSTRACT FROM AUTHOR]

The carboxylate species Mo(NR)(CHCMe 2R′)(O 2CCPh 3) 2(R = various aryl groups or 1-adamantyl; R′ = Ph or Me) have been synthesized by salt metathesis between Mo(NR)(CHCMe 2R′)(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)(CHCMe 2Ph)(O 2CR′′) 2(Ar = 2,6- i-Pr 2C 6H 3; R′′ = CPh 2Me, Si(SiMe 3) 3) and Na[Mo(NAd)(CHCMe 2Ph)(O 2CAr ′) 3] (Ar′ = 2,6-Me 2C 6H 3). Terphenylcarboxylate species Mo(NR)(CHCMe 2Ph)(O 2CTer) 2(Ter = 2,6-diphenyl-4-methylphenyl or 2,6-diphenyl-4-methoxyphenyl) were prepared through protonolysis of Mo(NR)(CHCMe 2R′)(Me 2Pyr) 2with TerCO 2H, 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)(O 2CCPh 3) 2(PMe 3) (Ar′′ = 2- t-BuC 6H 4) was obtained. Several of the triphenylacetate complexes are active initiators for the regioselective polymerization of diethyl dipropargylmalonate (DEPDM). [ABSTRACT FROM AUTHOR]

(Me 2CF 3CO) 2(Ar′N)WW(NAr′)(OCMe 2CF 3) 2(Ar′ = 2,6-Me 2C 6H 3) reacts immediately at room temperature with 1 equiv of CCl 4to give the sparingly soluble [W(OCMe 2CF 3) 2Cl] 2(μ-NAr′) 2. [W(NAr′)(OCMe 2CF 3) 2] 2forms 1:1 adducts with simple donor ligands such as PMe 3, PPhMe 2, and pyridine, in which the base is likely to be coordinated to a single W center. Addition of ethylene to [W(NAr′)(OCMe 2CF 3) 2] 2yields [W(NAr′)(OCMe 2CF 3) 2] 2(μ-C 2H 4), 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′)(OCMe 2CF 3) 2] 2(μ-C 2H 4) produces (OCMe 2CF 3) 2(Et)W(μ-NAr′)(μ-N-2-CH 2-6-MeC 6H 3)W(OCMe 2CF 3) 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′)(OCMe 2CF 3) 2] 2with 2-butyne yields [W(NAr′)(OCMe 2CF 3) 2] 2(μ-MeCCMe). Addition of 4 equiv of CH 3CN to [W(NAr′)(OCMe 2CF 3) 2] 2in benzene gives a mixture of two products, Aand B, which have the empirical formula W(NAr′)(OCMe 2CF 3) 2(CH 3CN), according to elemental analyses. Compound Bwas found to contain the [μ-NC(Me)C(Me)N] 4−ligand in an unsymmetric dimer in which one nitrogen of the [μ-NC(Me)C(Me)N] 4−ligand is bridging while the other is bound in a terminal fashion to one metal. Compound Ais proposed to be a Cs-symmetric structural isomer of Bin which the [N(Me)CC(Me)N] 4−ligand is symmetrically bridging the two metal centers. X-ray studies are reported for [W(OCMe 2CF 3) 2Cl] 2(μ-NAr′) 2, [W(NAr′)(OCMe 2CF 3) 2] 2(μ-MeCCMe), and B. [ABSTRACT FROM AUTHOR]

Tungsten alkylidene complexes that contain the 2,6-dichlorophenylimido ligand (NArCl), W(NArCl)(CHCMe3)(ORF6)2and W(NArCl)(CHCMe3)(Biphen)(THP) (ORF6OCMe(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)2with excess ethylene gave the tungstacyclobutane complex W(NArCl)(ORF6)2(C3H6), while reaction of W(NArCl)(CHCMe3)(ORF6)2with internal olefins gave the dimer, W(-NArCl)(ORF6)22. 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 (interalia) the dimeric, heterochiral methylidene complex, W(NArCl)(Biphen)(-CH2)2, which decomposed further to yield homochiral W(NArCl)(Biphen)2(-CH2CH2). Finally, W(NArCl)(Biphen)2(-CH2CH2) loses ethylene reversibly to yield W(NArCl)(Biphen)2, which could not be isolated in pure form. W(-NArCl)OC(CF3)2Me22, W(NArCl)(Biphen)(C3H6), W(NArCl)(Biphen)(C2H4)(THF), W(NArCl)(Biphen)(C4H6), W(NArCl)(Biphen)(-CH2)2, and W(NArCl)(Biphen)2(-CH2CH2) were characterized through X-ray studies. [ABSTRACT FROM AUTHOR]

Molybdenum olefin metathesis catalysts that contain aliphatic 1-phenylcyclohexylimido (NPhCy) and 2-phenyl-2-adamantylimido (NPhAd) groups and (S)-Biphen or (R)-Trip 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)(CHCMe2Ph)(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 analogues. [ABSTRACT FROM AUTHOR]