Carbene complexes. Part 11. Steric and conformational effects upon the transition-metal reactivity of electron-rich olefins and derived species; heteroatom-donor-olefin–metal (Cr0, Mo0, W0, or RhI) and 2-imidazoline-N-donor–metal complexes, and the crystal and molecular structure of tetracarbonyl[NN′N″N‴-tetramethylbi(imidazolidin-2-ylidene)-NN″]-chromium(0)

摘要: The electron-rich olefin [:[graphic omitted]R]2, LR2, (R = Me or Et), reacts thermally with (a)[Cr(CO)6], forming [Cr(CO)5LR][(1) (2)] cis-[Cr(CO)4(LR2),][(3) (4)] or(b)[Cr(η-C6H6)(CO)3], yielding [Cr(η-C6H6)(CO)2LMe], (5): [Cr(CO)5LMe], (1), forms the mixed ligand complexes cis-[Cr(AsPh3)(CO)4LMe], (6) cis-[Cr(CO)4{C(OMe)Me}LMe], (7), upon treatment AsPh3, LiMe and then MeOSO2F, respectively. related olefins omitted]Me]2(L′Me2) [:C(NMe2)2]2(tdae) do not afford carbene Cr0. From [M(CO)4(bhd)](M Cr, MO, W; bhd bicyclo[2.2.1]hepta-2,5-dtene) each of three readily affords heteroatom-donor-olefln species [M(CO)4(olefin-NN″)]. For M latter is transformed into N′N″-carbenemolybdenum complexes, only for LMe2, but L′Me2 tdae. Attempted in situ syntheses metal LH2 LH–LEt[from HC(OMe)2NMe2, H2NCH2CH2NH2 H2NCH2CH2NHEt, a MO0 RhI reagent] lead instead to 2-imidazoline [N[graphic omitted]H2](R H Et)N-bonded Mo0 RhI. Carbon-13 n.m.r. (but also i.r. 1H n.m.r.) spectra are diagnostic differentiating type complex (carbene, olefln-N,N″, imidazoline) its stereochemistry. crystal molecular structure [Cr(CO)4(LMe-NN″)] shows be an approximately octahedral environment: mutually-trans CO ligands bent away from fragment have Cr–C bond lengths 1.90 A compared 1.82 those cis; CC length 1.34 there probably little interaction Cr atom, distance closest approach being ca. 3.0 A.