Metal Alkoxides-Models for Metal Oxides. 6. The Linking of Alkyne and Nitrile Fragments at Ditungsten Centers. Preparation and Characterization of W2(O-t-Bu)6(CHCHC(Ph)N), W2(O-i-Pr)7(CH2CHC(Ph)N), W2(OCH2-t-Bu)6(N(CMe)4N)(py), and W2(O-i-Pr)7(NHC(Me)CHCHC(Me)N)

Article abstract of DOI:10.1021/ja00334a057

Alkyne adducts of ditungsten hexaalkoxides react in hydrocarbon solvents with nitriles to give novel dinuclear compounds containing five- or seven-membered heterocyclic rings.In W2(O-t-Bu)6(CHCHC(Ph)N), I, which is formed in the reaction between W2(O-t-Bu)6(μ-C2H2)(py) and PhCN (1 equiv), each tungsten atom is in a distorted trigonal-bipyramidal environment.The metal atoms are joined along a common equatorial-axial edge through the agency of an alkoxy ligand and the nitrogen atom of the metallacyclic ligand formed by the coupling of the alkyne and nitrile.Formally this ligand can be counted as a 4- ligand with terminal alkylidene and imido groups: <*>W=CHCH=C(Ph)N<*>=W, where W=C = 1.980(6) Angstroem, W-N = 2.041(5) Angstroem, and W=N = 1.903(5) Angstroem.The W-W distance is 2.674(1) Angstroem, indicative of a single bond.I reacts with 2-propanol to give W2(O-i-Pr)7(CH2CHC(Ph)N), II, which is the product of the combined reactions of alcoholysis and alcohol addition across the tungsten-carbon double bond: W=CH- + ROH -> POWCH2-.In II each tungsten atom is in a distorted octahedral environment and the two metal atoms share a face formed by two bridging OR ligands and the nitrogen atom of the metallacycle that is now formally a 3- ligand having imido and alkyl attachments to tungsten: W-C = 2.174(8) Angstroem, W-N = 1.980(6) and 1.962(7) Angstroem, and W-W = 2.585(1) Angstroem.In W2(OCH2-t-Bu)6(N(CMe)4N)(py), III, which is formed in the reaction between W2(OCH2-t-Bu)6(py)2(μ-C2Me2) and MeCN (>2 equiv), there is a seven-membered metallacycle that incorporates the 4-ligand derived from 1,4-diamino-1,2,3,4-tetramethyl-1,3-butadiene.The connectivity involves one terminal imido group, W-N = 1.78(1) Angstroem, and one bridging imido group, W-N(μ) = 1.90(1) and 2.09(1) Angstroem.Each tungsten atom is in a distorted octahedral environment, and the W-W distance 2.617(1) Angstroem corresponds to a M-M single bond.The compound W2(O-i-Pr)7(NHC(Me)CHCHC(Me)N), IV, is closely related to III.IV is formed in the reaction between W2(O-i-Pr)6(py)2(μ-C2H2) and MeCN (>2 equiv) in the presence of i-PrOH.The seven-membered metallacycle now has a terminal amido group (1-) and a bridging imido (2-) function, and the addition of ROH across the W=N bond parallels the conversion of I to II.W-N(amido)= 1.986(8) Angstroem; W-N (μ-imido)=1.983(8) and 2.007(8) Angstroem.Each tungsten is in a distorted octahedral environment with the W-W distance = 2.576(1) Angstroem.The compounds I through IV have been characterized by variable-temperature 1H and 13C NMR spectroscopy: I, II, and IV are fluxional.Crystal data for I at -158 deg C: a=19.237(8) Angstroem, b=10.619(4) Angstroem, c=10.180(3) Angstroem, α=111.97(2) deg, β=97.26(2) deg, γ=73.00(2) deg, Z=2, d_calcd=1.685 g cm^-3, and space group P1.Crystal data for II at -152 deg C: a=18.346(3) Angstroem, b=11.579(1) Angstroem, c=10.180(1) Angstroem, α=107.08(1) deg, β=61.54(1) deg, γ=98.19(1) deg, Z=2, d_calcd=1.666 g cm^-3, and space group P1.Crystal data for III at -168 deg C: ......