Chemistry of di- and tri-metal complexes with bridging carbene or carbyne ligands. Part 41. Synthesis of alkylidynetungsten complexes with (pyrazol-1-yl)borato ligands; crystal structures of [W(CC6H4Me-4)(CO)2{B(pz)4}], [Rh2W(µ3-CC6H4Me-4)(µ-CO)(CO)2(η-C9H7)2{HB(pz)3}]·CH2Cl2 and [FeRhW(µ3-CC6H4Me-4)(µ-MeC2Me)(CO)4(η-C9H7){HB(pz)3}]

Abstract

Reactions between the poly(pyrazol-1-yl)borato-salts K[R′B(pz)₃](pz = C₃H₃N₂; 1a, R′= C₃H₃N₂; 1b, R′= H) and the bromo(alkylidyne)tungsten complexes [W(CR) Br(CO)₄] afford the compounds [W(CR)(CO)₂{R′B(pz)₃}](2a, R = C₆H₄Me-4, R′= C₃H₃N₂; 2b, R = C₆H₄Me-4, R′= H; 2c, R = Me, R′= H). The structure of (2a) has been established by X-ray diffraction. The tungsten atom is in an essentially octahedral environment ligated by two CO groups, the alkylidyne fragment CC₆H₄Me-4 [CW 1.821(7)Å], and the [B(pz)₄]^– anion functioning as a tridentate ligand. Interestingly, the three N-W distances in the latter are not equal, that trans to the alkylidyne carbon being significantly longer [2.284(6)Å] than those traps to the CO ligands [2.219(6) and 2.186(5)Å]. The compounds (2) have been used to prepare the cluster complexes [Co₂W(µ₃-CR)(CO)₈-{R′B(pz)₃}][3a, R = C₆H₄Me-4, R′= C₃H₃N₂; 3b, R = C₆H₄Me-4, R′= H; 3c, R = Me, R′= H), [RhW(µ-CC₆H₄Me-4)(CO)₃(η-C₉H₇){HB(pz)₃}](4), [Rh₂W(µ₃-CR)(µ-CO)(CO)₂(η-C₉H₇)₂{HB(pz)₃}](5a, R = C₆H₄Me-4; 5b, R = Me), [FeRhW(µ₃-CR)(µ-CO)(CO)₅(η-C₉H₇){HB(pz)₃}](6a,R = C₆H₄Me-4; 6b, R = Me), and [PtW(µ-CC₆HaMe-4)(CO)₂(L)(PMe₃){HB(pz)₃}](8a, L = PMe₃; 8b, L = CO). The structure of (5a) was determined by X-ray diffraction. The almost isosceles metalatom triangle [Rh–Rh 2.646(2), Rh–W mean 2.848 Å] is capped by the tolylmethylidyne group [µ₃-C–Rh mean 2.072, µ₃-C–W 2.010(6)Å]. The Rh–Rh bond is symmetrically bridged by a CO ligand, and the two carbonyl groups on tungsten semibridge the two Rh–W bonds [W–C–O 168.0(6) and 164.5(6)°]. The indenyl group attached to each rhodium shows slippage to an η³-bonding mode. The tridentate tris(pyrazol-1-yl)borato ligand is co-ordinated to the tungsten with the N–W separation [2.245(5)Å]transoid to the alkylidyne carbon being somewhat longer than the other two N–W distances [mean 2.222 Å]. The trimetal compounds (6) react with but-2-yne to give the alkylidyne- and alkyne-bridged complexes [FeRhW(µ₃-CR)(µ-MeC₂Me)(CO)₄(η-C₉H₇){H B(pz)₃}](7a, R = C₆H₄Me-4; 7b, R = Me); the structure of (7a) being established by X-ray diffraction. The metal atoms form a triangle [Fe–Rh 2.577(2), Fe–W 2.756(2), Rh–W 2.677(2)Å] the face of which is bridged asymmetrically by the µ₃-CC₆H₄Me-4 ligand [µ₃-C–Fe 1.926(3), µ₃-C-Rh 2.202(4), µ₃-C–W 2.042(4)Å]. The Rh–W edge is bridged transversely on the opposite face of the triangle by the MeCCMe ligand. The iron atom carries three terminal carbonyl groups, while the remaining CO attached to the tungsten semibridges the Fe–W bond [W–C–O 165.3(4)°]. The [HB (pz)₃]^– ligand is bonded to the tungsten with three essentially equal N–W distances, while the indenyl group on the rhodium shows the customary slippage towards η³ bonding. The spectroscopic properties (i.r. and n.m.r.) of the new compounds are reported and discussed.