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The synthesis of (CN)Pt^II(acac) complexes (CN = benzo[h]quinoline, 8-methylquinoline) and their oxidation with PhI(OAc)2 are reported as a model system for palladium-catalyzed C−H bond functionalization. Dimeric Pt^III−Pt^III complexes containing a bridging acetate ligand are obtained in HOAc, and monomeric Pt^IV complexes incorporating alkoxide and acetate ligands are obtained in MeOH, EtOH, and iPrOH. The implications of these results for the mechanism of analogous Pd-catalyzed reactions is discussed.

1,2-Dihydro-2-phenyl-1,2-azaborine (6a) has been prepared by a multistep synthesis from the readily available 2,2-dibutyl-2,5-dihydro-1-trimethylsilyl-1H-1,2-azastannole (7). Deprotonation of 6a affords 1-phenyl-1,2-azaboratabenzene 1a, which on reaction with [Cp*RuCl]4 gives the sandwich compound 5. 5 has been shown to function as a nucleophilic catalyst for the acylation of benzyl alcohol by phenylethylketene.

Two general methods have been developed for the synthesis of alkali metal salts of 2-substituted-1,2-oxaborolides (6). 2-Phenyl-1,2-oxaborolide (6b) has been converted to RuCp* complex 11b and to Mn(CO)3 complex 12b, in which the metals are η⁵-bound to the ligand.

The reaction of (Et3P)2Pd(μ-S)Ge[N(SiMe3)2]2 (2) with paraformaldehyde under photolytic conditions results in the insertion of formaldehyde into the Pd−Ge bond, with bond cleavage, to give (Et3P)2Pd(μ-S)(μCH2O)Ge[N(SiMe3)2]2 (3). Subsequent addition of CO to 3 results in migratory insertion into the Pd−C bond, followed by rapid reductive elimination to regenerate the Pd⁰ metal center and give a unique five-membered organic heterocycle, Ge[N(SiMe3)2]2SC(O)CH2O (6). The X-ray crystal structure of the dppe (dppe = bis(diphenylphosphino)ethane) derivative of 3, (dppe)Pd(μ-S)(μCH2O)Ge[N(SiMe3)2]2 (4), is reported.

The sequential reaction of 9-fluorenyllithium and CpNa with (ⁱPr)2NBCl2 followed by the sequential treatment with LDA and ZrCl4 afforded [(η⁵-C13H8)BN(ⁱPr)2(η⁵-C5H4)ZrCl2 (2e). The structure of 2e was determined by X-ray diffraction, which shows that the molecule has Cs symmetry. On activation by excess methylaluminoxane (MAO) 2e was converted to an active catalyst for polymerization of ethylene and propylene. The polypropylene is syndiotactic (81% rr triads).

Herein we report the CH insertion of a stable germylene, Ge[CH(SiMe3)2]2, into the α-CH bonds of the acetyl-containing ketones acetone, butanone, and cyclopropyl methyl ketone. This CH insertion reaction requires the presence of MgCl2, yet the reaction can be successfully carried out in hydrocarbon, aromatic, and ethereal solvents. In the absence of MgCl2, these acetyl-containing ketones do not undergo CH insertion but instead undergo an OH insertion to give a germyl vinyl ether. A number of other ketones, including the acetyl-containing pinacolone, have been observed to only undergo insertion into the OH bond even in the presence of MgCl2.

Ge[CH(SiMe3)2]2 (1) and Ge[N(SiMe3)2]2 (2) react with anthraquinone and naphthoquinone in a 2:1 ratio to form five-membered rings with the carbonyl oxygens and the ortho carbons of the adjacent aromatic ring. The reaction with 1,4-diacetylbenzene proceeds in a similar fashion with 1; however no reaction is observed with 2. Compounds 1 and 2 react with 1,2-diacetylbenzene to yield a novel bicyclo species. In a previous report describing equilibria between 1 and phenones, it appeared that 2 did not undergo reaction to generate the five-membered ring with the accompanying formation of a conjugated triene. However, these quinone results indicate that an equilibrium can exist between 2 and a phenone moiety. In the reaction with quinones, a second equivalent of germylene effectively traps the conjugated triene by undergoing a 1,4-addition reaction. Unlike the initial triene formation, this second insertion is irreversible.

The reaction of 1,1-dibutyl-1-stannacyclohexa-2,5-diene (8) with 1,2-bis(dichloroboryl)benzene 9 affords exchange product 10, which on deprotonation followed by reaction with ZrCl4 gives the very labile o-phenylene-bridged bis(1-boratabenzene)zirconium dicholoride 6. A similar reaction sequence from 8 and 1,1-bis(dichloroboryl)-2-methyl-1-propene 11 affords the 1,1-isobutenyl-bridged bis(1-boratabenzene)zirconium dichloride 7. The X-ray structure of 7 is described.

The synthesis of three novel Pd germylene complexes is reported. (Ph3P)2PdGe[N(SiMe3)2]2 (1) was synthesized by ligand substitution of (Ph3P)4Pd, whereas (Et3P)PdGe[N(SiMe3)2]2 (2) and {dppePdGe[N(SiMe3)2]2}2 (3b) (dppe = (diphenylphosphino)ethane) were synthesized by photolytic reduction of their corresponding phosphine oxalato complexes followed by addition of the germylene ligand. In solution, 3b exists in equilibrium with the monomeric dppePdGe[N(SiMe3)2]2 (3a). The germylene ligand of 2 was found to be 1 order of magnitude more labile than the analogous Pt system and 2 orders of magnitude less labile than the analogous Ni system. The reactivity of these new palladium germylenes toward O2 is described.

1,2-Dihydro-1,2-azaborines (1c, 1d, and 1e) have been prepared by the reaction of the corresponding 2,3-dihydro-1H-1,2-azaborol-3-yllithium reagents (1c, 1d, and 1e). The reaction of 1e with Py3Mo(CO)3 and BF3·OEt2 affords Mo(CO)3 complex 5e, while the reaction of 1c with Cr(CH3CN)3(CO)3 affords Cr(CO)3 complex 6c. X-ray structures of 5e and 6c show that the metals are η⁶-bound to the 1,2-dihydro-1,2-azaborine rings.

1-Arsanaphthalene (3) and 2-trimethylsilyl-1-arsanaphthalene (4) have been prepared from the corresponding 1,4-dihydro-1,1-dimethyl-1-stannanaphthalenes 7 and 17, respectively, via an exchange reaction with AsCl3 followed by dehydrohalogenation by DBU. Both 3 and 4 are in mobile equilibrium with their head-to-head Diels−Alder dimers. The reaction of 4 with Mo(CO)3(Py)3 and BF3·OEt2 affords Mo(CO)3 complex 5. The crystal structure of 5 shows that the Mo(CO)3 group is η⁶-bound to the C5As ring of the arsanaphthalene.

The reaction of 1-chloro-1-boracyclohexadiene (12) with N,N‘-dimethyl-N,N‘-bis(trimethylsilyl)ethylene-1,2-diamine followed by LDA afforded the dilithium salt of N,N‘-bis(1-boratabenzene)-N,N‘-dimethylethylene-1,2-diamine (14). The reaction of 14 with ZrCl4 afforded the boron-bridged dimethylethylenediamino bis(boratabenzene) zirconium dichloride complex 8, while reaction of 14 with FeCl2 afforded the corresponding dimethylethylenediamino-bridged iron(II) complex 9. The structures of 8 and 9 were determined by X-ray diffraction. In each case the boratabenzene units are bridged by an approximately C2-symmetric dimethylethylenediamino bridge which makes 8 and 9 chiral. A barrier to interconversion of the enantiomeric conformers of 8 was determined by 2D ¹H NOESY as 21.2 ± 0.2 kcal/mol, while the corresponding barrier of 9 was determined from variable-temperature ¹³C NMR spectroscopy to be 16.9 ± 0.5 kcal/mol. Both barriers involve rotation about the exocyclic B−N π-bonds. Comparison has been made with the corresponding bridged cyclopentadienyl complexes 10 and 11.

A new transition metal germylene complex, (Ph3P)2NiGe[2,4,6-(CF3)3C6H2]2 (2), has been synthesized and structurally characterized. The metrical parameters of complex 2 are compared and contrasted with the previously synthesized complexes (Ph3P)2NiGe[N(SiMe3)2]2 (3) and (Et3P)2PtGe[N(SiMe3)2]2 (1). Nonlocal BP86 density functional calculations support the presence of Ni−Ge d−p π bonding in complexes 2 and 3.

1,4-Dihydro-1,1-dimethyl-1-stannanaphthalene (10) has been prepared by a multistep synthesis starting from α,2-dibromotoluene (6). The reaction of 10 with MeBBr2 followed by LDA afforded lithium 1-methyl-1-boratanaphthalene (2a). The reaction of 10 with BCl3, followed by diisopropylamine and subsequent treatment with LDA, gave lithium N,N-diisopropyl-1-amino-1-boratanaphthalene (2c). The boratanaphthalenes have been characterized using ¹H NMR, ¹¹B NMR, and ¹³C NMR spectroscopy. The pKa of the conjugate acid of 2c is close to that of indene. 2a reacts with [Cp*RuCl]4 to form Ru sandwich compound 4a, in which the boratanaphthalene is η⁶ bound to Ru. 2c reacts with Cp*ZrCl3 to form a Cp*ZrCl2 adduct 5c, in which the boratanaphthalene unit is unsymmetrically bound to Zr.

The reaction of 1-chloro-1-boracyclohexa-2,5-diene with (3-(dimethylamino)propyl)magnesium chloride followed by reaction with tert-butyllithium in ether affords lithium 1-(3-(dimethylamino)propyl)boratabenzene (8). The reaction of 8 with Mn(CO)3(CH3CN)3PF6 affords tricarbonyl[1-(3-(dimethylamino)propyl)boratabenzene]manganese(I) (15B). The crystal structure of 15B shows that it exists in the intramolecularly B−N-coordinated form with a B−N bond distance of 1.716(5) Å. However in toluene-d8 solution 15B is in mobile equilibrium with its ring-opened isomer 15A. Using ¹¹B NMR spectroscopy the equilibrium constants for 15B → 15A have been measured over the temperature range −35 to 48 °C, allowing evaluation of ΔH° (6.0 kcal/mol) and ΔS° (23 cal/mol K).

A series of new bimetallic sulfido clusters, Cp^#2M2M‘2S4(NO)2 (Cp^# = C5Me2Et, C5Me5, C5H5; M = Mo, W; M‘ = Fe, Co) have been synthesized and characterized by X-ray diffraction. Two new tungsten carbonyl clusters, Cp*2W2Co2S4(CO)2 and Cp^Et2W2Co2S3(CO)5, were also synthesized and the structure of the latter determined. The structural systematics are related to the redox properties and to the electronic structure of the clusters.

The paramagnetic cluster anions Cp‘2Mo2Co2S4(CO)2^- (6), and Cp*2Mo2Co2S4(CO)2^- (6*) were prepared by the reaction of Cp‘2Mo2Co2S3(CO)4 with p-toluene thiolate or by Na amalgam reduction of the cubane Cp*2Mo2Co2S4(CO)2 (Cp* = C5Me4Et), respectively. The CO-substituted cluster Cp‘2Mo2Co2S3(CO)3(SAr)^- (7) was a minor byproduct in the synthesis of 6. The X-ray crystal structures of these anionic clusters were determined. The effects of the addition or removal of electron density from the cluster core on the cluster structure is presented.

The reaction of 1-chloro-1-boracyclohexa-2,5-diene with diisopropylamine or N-benzyl-N-methylamine followed by reaction with LDA in THF affords lithium N,N-diisopropyl-1-aminoboratabenzene (9b) or lithium N-benzyl-N-methyl-1-aminoboratabenzene (9c), respectively. The reaction of 9b with FeCl2 affords bis(N,N-diisopropyl-1-aminoboratabenzene)iron (18b), while the reaction of 9b or 9c with Mn(CO)3(CH3CN)3PF6 affords tricarbonyl[N,N-diisopropyl-1-aminoboratabenzene)manganese (19b) or tricarbonyl-1-(N-benzyl-N-methylamino) boratabenzene manganese (19c), respectively. Photochemical displacement of CO by PMe3 from 19b affords dicarbonyl(trimethylphosphine) (N-benzyl-N-methyl-1-aminoboratabenzene)manganese (20b). The rates of bond rotation about the B−N bonds of 9c, 18b, 19b,c, and 20b have been determined using variable-temperature NMR spectroscopy. The rates depend markedly on the electron-withdrawing power of the coordinating metal group. The boron atom is weakly coordinated to manganese (B−Mn = 2.485(3) Å) and strongly bound to nitrogen (B−N = 1.417 (3) Å).

A series of o-(trifluoromethyl)phenyl-substituted germanes have been synthesized to study the potential for weak Ge−F bonding interactions. ¹H−¹⁹F coupling constants in these compounds range between 2 and 5 Hz. These coupling magnitudes are consistent with previously reported literature examples in ¹⁹F and multinuclear NMR spectra for derivatives of the [2,4,6-(CF3)3C6H2]− ligand. Solid-state structural characterization of these germanes consistently reveals Ge−F contacts at 2.8−2.9 Å, midway between the longest single bond and the longest expected van der Waals contact. For the simple unsymmetrical catenate, [3,5-(CF3)2C6H3]2Ge(H)Ge(H)[2,4,6-(CF3)3C6H2]2 (4), there are close contacts to both germanium atoms from the ortho-CF3 groups. 4 is not otherwise sterically constrained to force distal, intramolecular contacts, and thus a weak Ge−F bonding interaction is invoked for the entire series of o-(trifluoromethyl)aryl-substituted tetravalent Ge compounds. The synthetic approaches to these germanes make extensive use of Ge(II) precursors, employing both catalytic hydrogenation and insertion reactions of germylenes.

Ethylene-bridged bis(N,N-diisopropyl-1-aminoboratabenzene-4-yl)zirconium dichloride (5a), dimethylsilyl-bridged bis(N,N-diisopropyl-1-aminoboratabenzene-4-yl)zirconium dichloride (7a), and dimethylmethylene-bridged (cyclopentadienyl)(N,N-diisopropyl-1-aminoboratabenzene-4-yl)zirconium dichloride (6a) have been prepared. X-ray crystal structures of the dimethyl derivatives of 5 and 7 show that the complexes closely resemble the corresponding ansa-zirconocenes. When activated by excess methylaluminoxane, 5a, 6a, and 7a are catalysts for the polymerization of olefins.

The heterobimetallic sulfido cluster Cp^Et2Mo2Co2S4(CO)2 was oxidized to give a series of 58-VSE (valence shell electron) electron-deficient clusters of the type Cp^Et2Mo2Co2S4(X)2 (X = I, Br, Cl, SPh). These clusters have been structurally characterized by X-ray diffraction. Their magnetic behavior was investigated to reveal complex spin equilibria for the halide-substituted clusters (X = I, Br, Cl) and simple paramagnetism for the thiolate substituted cluster (X = SPh). In an attempted catalytic reaction, Cp^Et2Mo2Co2S4(CO)2 reacted with excess benzene thiol under 1000 psi of CO at 150 °C to give phenylthiobenzoate, PhS(CO)Ph, and PhSSPh in excess of the stoichiometric amounts.

Treatment of the heterobimetallic sulfido cluster Cp‘2Mo2Co2S3(CO)4 (1) with the diphosphine compound bis(diphenylphosphino)methane (dppm) or bis(diphenylphosphino)ethane (dppe) gives the carbonyl-substituted adduct Cp‘2Mo2Co2S3(CO)2(η²-dppm) (11a) or Cp‘2Mo2Co2S3(CO)2(η²-dppe) (11b), respectively, whereas treatment of 1 with an excess of bis(dimethylphosphino)ethane (dmpe) gives the cluster Cp‘2Mo2Co2S3(μ3-CO)(η²-dmpe)2 (12) containing a triply-bridging carbonyl ligand (νCO = 1615 cm^-1). Cluster 12 readily reacts with dichloromethane to give the μ3-methylidyne cluster [Cp‘2Mo2Co2S3(μ3-CH)(η²-dmpe)2]⁺ (14). Cluster 14 was also characterized by an X-ray crystallographic analysis. Reaction of ¹³CO-labeled 12 with CH2Cl2 and CD2Cl2 showed that the methylidyne atoms originate from the dichloromethane solvent. ¹³CO-labeled 1 was prepared to 96% enrichment and revealed a resonance for the carbonyl ligands in the ¹³C-NMR spectrum at δ 207 with w1/2 = 940 Hz. Cluster 11b was found to desulfurize thiols and perform phosphinidene abstraction reactions via formation of the monomeric cluster Cp‘2Mo2Co2S4(η²,μ2-dppe) (18) or the oligomeric clusters [Cp‘2Mo2Co2S3(μ3-PPh)(η²,μ2-dppe)]n (19), respectively.

The reaction of 1-substituted borepins C6H6BX, where X = Me, Ph, and Cl, with Py3Mo(CO)3 and BF3·OEt2 affords the corresponding borepin molybdenum tricarbonyl complexes. Similar reaction of 1-methoxyborepin affords (C6H6BF)Mo(CO)3. The reaction of (C6H6BCl)Mo(CO)3 with appropriate nucleophiles affords the boron-substituted complexes (C6H6BX)Mo(CO)3, where X = H, OCH3, OH, O1/2, N(iPr)2, N(CH2)5, N(c-C6H11)2, and NBnMe. All complexes (C6H6BX)Mo(CO)3 have been compared using ¹H NMR, ¹¹B NMR, and ¹³C NMR spectroscopies. The X-ray structure of (C6H6BN(iPr)2)Mo(CO)3 shows that Mo is η⁶-coordinated to the ring carbon atoms but not to B. Rates of rotation about the B−N bonds of (C6H6BN(iPr)2)Mo(CO)3 and (C6H6BNBnMe)Mo(CO)3 have been measured using variable-temperature NMR spectroscopy.

The dialkylgermylene [Ge(CH[SiMe3]2)2] (3) converts the carbene complexes [Ru(CHR)(PCy3)2Cl2] (R = p-C6H4Me [2], n-C4H9 [6]) into the corresponding square-planar carbyne complexes [Ru(CR)(PCy3)2Cl] (R = p-C6H4Me [1], n-C4H9 [7]) cleanly within minutes at 25 °C in benzene; addition of HCl to a benzene solution of 1 results in quantitative re-formation of 2. Replacement of chloride in 1 affords other halide and pseudohalide complexes, [Ru(C-p-C6H4Me)(PCy3)2X] (X = p-OC6H4-t-Bu, Br, F, O3SCF3), cleanly.

Ge[CH(SiMe3)2]2 reacts with benzophenone to form a conjugated triene. Wilkinson's catalyst, Rh(PPh3)3Cl, is an effective precatalyst for the isomerization of one double bond and hydrogenation of a second double bond of this triene. This reaction demonstrates that germylene activation of the phenone moiety yields reactive double bonds amenable to catalytic transformation, even with bulky catalysts such as the presumed active form of Wilkinson's catalyst, Rh(PPh3)2Cl.

The reaction of 1,4-dihydro-4-(diisopropylamino)-2,6-dimethyl-1-phenyl-1,4-phosphaborin (6) with Mn2(CO)10 affords 7, the Mn(CO)3 complex of 4-(diisopropylamino)-2,6-dimethyl-1,4-phosphaboratabenzene. Reaction of 6 with Li followed by [Cp*RuCl]4 gives the ruthenium(II) complex 8. Crystal structures of 6−8 have been determined.

The fused-ring diheteroaromatic 3a,7a-azaborindenyl anion (1) has been prepared by a synthesis using the Grubbs ring-closing metathesis. 1 has been converted to the Cp*ZrCl2 complex 2, which closely resembles the corresponding (Ind)Cp*ZrCl2.

The germylene Ge[CH(Si(CH3)3)2]2 reacts with phenones to give conjugated trienes. This reaction is quantitative at room temperature in minutes and has some functional group tolerance.

The heteroaromatic anion lithium 2-(diisopropylamino)-1,2-thiaborolide (3) has been prepared by a synthesis using the Grubbs ring-closing metathesis. 3 has been converted to the Cp*Ru complex 10, the Cp*ZrCl2 complex 11, and the Me2Si-bridged CpZrCl2 complex 15.

The reaction of 2-methylbenzenethiol with 2 equiv of BuLi followed by (i-Pr)2NBCl2 affords 2,3-dihydro-2-(diisopropylamino)-1,2-benzothiaborole (10), which can be deprotonated by t-BuLi to form lithium 2-(diisopropylamino)-1,2-benzothiaborolide (3). The benzothiaborolide was converted to the Cp*ZrCl2 complex 11 and the Cp*Ru complex 12, in which the thiaborolide ring is η⁵-coordinated to Ru.

Novel aminoboranediyl-bridged zirconocenes [i-Pr2NB(η⁵-C5H4)2]ZrCl2 (8b) and [i-Pr2NB(η⁵-1-C9H8)2]ZrCl2 (4b) have been prepared and structurally characterized. When activated by excess methylaluminoxane, 4b and 8b form highly active catalysts for the polymerization of ethylene. The catalyst derived from 4b converts propylene to isotactic polypropylene.

(4-Dimethylsilyl-tert-butylamido)-N,N-diisopropyl-1-aminoboratabenzene ZrCl2 (7a) and TiCl2 (7b) complexes have been prepared. When activated by excess methylaluminoxane, 7a and 7b are catalysts for the polymerization of ethylene.

1,4-Diphenyl-1,3-butadiyne readily displaces PMe3 from bis(N,N-diisopropyl-1-amino-1-boratabenzene)bis(trimethylphosphine)zirconium(II) to afford a 1:1 adduct which contains a 2,5-diphenyl-1-zirconacyclopenta-2,3,4-triene unit.

Lithium N,N-diisopropyl-3-amino-1,3-benzothiaborolide (5) was prepared by a multistep synthesis starting from thioanisole. The thiaborolide 5 was converted to a Cp*Ru η⁵-adduct, which was characterized by X-ray diffraction.

The fluoroarylgermylene bis[2,4,6-tris(trifluoromethyl)phenyl]germanium(II) was synthesized by the reaction of 2 equiv of [2,4,6-tris(trifluoromethyl)phenyl]lithium with GeCl2·dioxane. This monomeric germylene has good thermal stability, despite having the least sterically encumbering set of stabilizing ligands of any alkyl germylene isolated to date.

The reaction of 2 equiv of lithium 1-phenylboratabenzene with ZrCl4 in ether affords bis(1-phenylboratabenzene)zirconium dichloride (2), while [4-tert-C4H9C5H4BPh]2ZrCl2 (3), obtained in a similar manner, was subjected to a single-crystal X-ray diffraction study. The reaction of a solution of 2 and methylaluminoxane (MAO) with C2H4 (1 atm, 25 °C) affords ethylene oligomers (dimers of 1-alkenes as the major product, together with minor amounts of 1- and 2-alkenes).

Reaction of Hf*Cl2 (1; Hf* = decamethylhafnocene), with excess sodium acetylide at room temperature results in the synthesis of Hf*(CCH)2 (2). The identical reaction in refluxing THF results in the dimeric product [(μ2-C2)(Hf*CCH)2] (4). Subsequent reaction of 2 with lithium diisopropylamide (LDA) in the presence of trimethyltin chloride resulted in the trimetallic Hf*(CCSnMe3)2 (3).