Conversion of a µ3-alkylidyne into a µ3-acyl group at a trimetal centre; X-ray crystal structures of the phosphido bridged complexes [WFe2(µ3-CR)(µ-H)(µ-PEt2)(CO)6(PEt2H)(η-C5H5)]·Et2O, [WFe2(µ3-CR)(µ-PPh2)2(CO)6(η-C5H5)]·0.5 CH2Cl2, [WFe2(µ3-OCCH2R)(µ-PPh2)2(CO)5(η-C5H5)], and [WFe2(µ-OCCH2R)(µ-PPh2)2(CO)6(PPh2H)(η-C5H5)]·CH2Cl2(R = C6H4Me-4)

Abstract

In diethyl ether at room temperature the complex [WFe₂(µ₃-CR)(µ-CO)(CO)₈(η-C₅H₅)](1)(R = C₆H₄Me-4) reacts with 1 equivalent of PMe₂Ph or PEt₂H affording the compounds [WFe₂(µ₃-CR)(µ-CO)(CO)₇(PR′₃)(η-C₅H₅)][PR′₃= PMe₂Ph (2) or PEt₂H (3)]. At ambient temperature solutions of (3) slowly (1–2d) lose CO giving the µ-PEt₂ complex [WFe₂(µ₃-CR)(µ-H)(µ-PEt₂)(CO)₇(η-C₅H₅)](4), which exists as a mixture of isomers in which the hydride ligand bridges either a W–Fe (4a) or an Fe–Fe (4b) bond. In solution (4a) and (4b) interconvert slowly on the n.m.r. time-scale. The reaction between (1) and an excess of PEt₂H gave [WFe₂(µ₃-CR)(µ-H)(µ-PEt₂)(CO)₆(PEt₂H)(η-C₅H₅)]·Et₂O (5). The structure of (5) was established by a single-crystal X-ray diffraction study and consists of a WFe₂ triangle of metal atoms capped by a µ₃-CR ligand [W–Fe(1) 2.763(1), W–Fe(2) 2.830(1), Fe(1)–Fe(2) 2.687(2), W–µ-C 2.042(8), Fe(1)–µ-C 1.960(8), and Fe(2)–µ-C 2.104(8)Å]. One W–Fe bond is bridged by a µ-PEt₂ group and the Fe–Fe bond is bridged by an hydride ligand. The tungsten atom carries a CO and C₅H₅ group. One iron atom is ligated by two CO groups and a terminal PEt₂H ligand which is trans to the µ-PEt₂ group, the remaining iron atom carries three approximately orthogonal CO ligands. Thermolysis of (5) results in loss of H₂ and formation of the compound [WFe₂(µ₃-CR)(µ-PEt₂)₂(CO)₆(η-C₅H₅)](6). The conversion of (5) into (6) may be more readily achieved at room temperature by the addition of a catalytic amount of Li[BEt₃H]. The related reaction of complex (1) with 1 equivalent of PPh₂H gave [WFe₂(µ₃-CR)(µ-H)(µ-PPh₂)(CO)₇(η-C₅H₅)](7), which has the same structure as the µ-PEt₂ isomer (4a). Treatment of (1) with an excess of PPh₂H afforded a chromatographically separable mixture of the cluster compounds [WFe₂(µ₃-CR)(µ-PPh₂)₂(CO)₆(η-C₅H₅)]·0.5CH₂Cl₂(8), [WFe₂(µ₃-OCCH₂R)(µ-PPh₂)₂(CO)₅(η-C₅H₅)](9), and [WFe₂(µ-OCCH₂R)(µ-PPh₂)(CO)₆(PPh₂H)(η-C₅H₅)]·CH₂Cl₂(10). The molecular structures of (8)–(10) have been established by single-crystal X-ray diffraction studies. The structures of both (8) and (9) consist of WFe₂ triangles of metal atoms with W–Fe and Fe–Fe bonds bridged by µ-PPh₂ ligands. The iron atoms all have two terminal CO ligands and the tungsten atoms are ligated by one CO ligand and a C₅H₅ group. In addition a W–Fe bond in complex (8) is semibridged by a CO ligand [Fe(2)–C(1) 1.791 (7)Å, Fe(2)–C(1)–O(1) 159.4(8)°]. In compound (8) the metal triangle is capped by a µ₃-CR group [W–µ-CR 2.085(6), Fe–µ-CR 1.989(6) and 2.052(6)Å]. In contrast, the metal triangle in (9) is capped by a µ₃-OCCH₂R moiety which is η² bound to the tungsten atom with σ attachments to the two iron atoms [W–O 2.129(6), W–C 2.155(7), Fe(1)–C 1.913(10), and Fe(2)–O 2.011 (6)Å]. Formation of complex (9) from (1) involves the transfer of two hydrogen atoms from terminal PPh₂H ligands to the µ₃-CR ligand, followed by migration of the resulting µ-CH₂R group to metal-bound CO. The structure of (10) consists of a W–Fe(2)–Fe(1) chain of metal atoms which arises via cleavage of a W–Fe bond in (1). The W–Fe(2) and Fe(2)–Fe(1) bonds are bridged by µ-PPh₂ ligands and a PPh₂H ligand is attached to Fe(1). The tungsten atom carries two CO ligands and a C₅H₅ group, and each iron atom has two terminal CO ligands. The Fe–Fe bond is bridged by a µ-OCCH₂R group [Fe(2)–O 2.038(3), Fe(1)–C 1.936(4)Å]. 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.