Synthesis and reactions of co-ordinatively unsaturated µ3-alkylidyne clusters; X-ray crystal structures of the phosphido bridged complexes [WFe2(µ3-CR)(µ-H)(µ-PPh2)(CO)6(η-C5H5)]and[WFe2(µ3-CR){µ-C(O)C(Me)CHMe}(µ-PEt2)(CO)5(η-C5H5)](R = C6H4Me-4)

Abstract

Thermal decarbonylation (toluene, 111 °C) of the complexes [WFe₂(µ₃-CR)(µ-H)(µ-PR′₂)(CO)₇(η-C₅H₅)][R = C₆H₄Me-4,R′= Ph (2) or Et (3)] gives good yields of the co-ordinatively unsaturated, 46 cluster valence electron derivatives [WFe₂(µ₃-CR)(µ-H)(µ-PR₂′)(CO)₆(η-C₅H₅)][R′= Ph (4) or Et (5)]. The structure of the µ-PPh₂ complex (4) was established by a single-crystal X-ray diffraction study and consists of a WFe₂ triangle of metal atoms [W–Fe(1) 2.817(1), W–Fe(2) 2.523(1), and Fe(1)–Fe(2) 2.569(1)Å] capped by a µ₃-CC₆H₄Me-4 group. The W–Fe(2) bond is bridged by a µ-PPh₂ ligand [W-µ–P 2.357(1), Fe(2)-µ–P 2.219(1)Å] whilst a hydride ligand, which was located and refined, bridges the homonuclear Fe–Fe bond [Fe(1)–H(1) 1.73(4), Fe(2)-H(1) 1.54(6)Å]. The tungsten atom carries a cyclopentadienyl ring and a terminal CO ligand. The Fe(2) centre bound to phosphorus has two terminal CO ligands, whilst the remaining Fe(1) atom has three approximately orthogonal terminal CO groups. The µ-PPh₂ bridged W–Fe(2) separation of 2.523(1)Å is extremely short. This suggests the presence of appreciable multiple-bond character in the W–Fe(2) bond which is consistent with the formulation of (4) as a co-ordinatively unsaturated complex. Spectroscopic data for complexes (4) and (5) reveal that in solution the hydride ligand adopts a terminal site on the Fe(1) atom. This contrasts with the bridging Fe(µ-H)Fe interaction observed in the solid state for (4). Solutions of (4) and (5) react with CO (15 min, 20 °C) to regenerate their saturated precursors (2) and (3) respectively. Dichloromethane solutions of (4) and (5) also react with alkynes (R″CCR″, R″= Me, Et, or Ph) to give the vinylacyl complexes [WFe₂(µ₃-CR){µ-C(O)C(R″)CHR″}(µ-PR₂′)(CO)₅(η-C₅H₅)][R′= Ph, R″= Me (6a), Et (6b), or Ph (6c); R′= Et, R″= Me (7)]. The molecular structure of the but-2-yne derivative (7) was established by a single crystal X-ray diffraction study. The structure consists of a WFe₂ triangle of metal atoms [W–Fe(1) 2.808(1), W–Fe(2) 2.679(1), and Fe(1)–Fe(2) 2.673(1)Å] capped by a µ₃-alkylidyne ligand. One W–Fe bond is bridged by a µ-PEt₂ ligand whilst the remaining W-Fe bond is bridged by a µ-C(O)C(Me)CHMe group which has been formed by coupling of hydride, but-2-yne, and CO ligands. The cis-{µ-C(O)C(Me)CHMe} ligand adopts a π-allyl η³-bonding mode to Fe(2)[Fe(2)–C(O) 2.083(5), Fe(2)–C(Me) 2.173(6), and Fe(2)–CHMe 2.186(6)Å], and the C(O) end of the chain uses an orthogonal set of orbitals to η² bond to the W atom [W–C(O) 2.011 (5), W–O 2.281 (4)Å]. Protonation of the complexes (6a) and (7)(CH₂Cl₂, HBF₄·Et₂O) occurs at the oxygen atom of the cis-{µ-C(O)C(Me)CHMe} ligand affording the unsaturated µ-allylidene derivatives [WFe₂(µ₃-CR){µ-C(OH)C(Me)CHMe}(µ-PR′₂)(CO)₅(η-C₅H₅)][BF₄][R′= Ph (8) or Et (9)]. The spectroscopic data (i.r. and ¹H, ¹³C-{¹H}, and ³¹P-{¹H} n.m.r.) for the new WFe₂ complexes are discussed and mechanisms are proposed to account for their formation.