Chemistry of the metal carbonyls. Part 79. Synthesis and X-ray crystal structures of [N(PPh3)2][Fe2Pt2(µ-H)(µ-CO)3(CO)5(PPh3)2], [Fe2Pt2(µ-H)2(CO)8(PPh3)2], and [Fe2Pt(CO)8(cyclo-C8H12)]

Abstract

Tetraethylammonium or bis (triphenylphosphine)iminium salts of the anion [Fe₂(µ-H)(µ-CO)₂(CO)₆]^– react with the complex [Pt(C₂H₄)₂(PPh₃)] in tetrahydrofuran to give the di-irondiplatinum compounds [R][Fe₂Pt₂(µ-H)-(µ-CO)₃(CO)₅(PPh₃)₂][R = NEt₄⁺ or N(PPh₃)₂⁺]. The structure of the N(PPh₃)₂⁺ salt was established by a single-crystal X-ray diffraction study; the crystals are monoclinic, space group P2₁/c, Z= 4, in a unit cell with lattice parameters a= 25.05(3), b= 14.28(1), c= 23.99(2)Å, and β= 106.84(7)°. The structure has been refined to R 0.059 (R′ 0.061) for 8 768 independent reflections to 2θ⩽ 50°[(Mo-K_α)X-radiation] collected at 200 K. The N (PPh₃)₂⁺ cation is bent [P–N–P 138.1(8)°], while the metal framework of the anion consists of a cluster of Fe₂Pt₂ atoms [Pt–Pt 2.966(1); Pt–Fe 2.756(2), 2.626(2), 2.555(2), and 2.562(2); Fe–Fe 2.522(2)Å], arranged such that a Fe₂ Pt triangle, edge-bridged by three CO ligands, is capped by a platinum atom carrying a terminal CO ligand and PPh₃ group. The four remaining CO ligands are terminally bonded in pairs to the two iron atoms, while the platinum atom in the triangle carries a PPh₃ group. Although not located in the X-ray diffraction study, evidence is presented that the hydrido-ligand bridges the longest of the four Fe–Pt separations. Protonation of the salts affords the neutral complex [Fe₂Pt₂(µ-H)₂(CO)₈(PPh₃)₂], also characterised by an X-ray diffraction study. Crystals are monoclinic, space group P2₁/c, Z= 4, in a unit cell with lattice parameters a= 10.83(2), b= 16.00(4), c= 27.88(4)Å, and β= 99.40 (11)°. The structure has been refined to R 0.056 (R′ 0.060) for 2 474 independent reflections to 2θ⩽ 40° at 200 K. The structure consists of an Fe₂Pt₂ core [Pt–Pt 2.998(2); Pt–Fe 2.696(3), 2.694(3), 2.631(3), and 2.604(3)Å], with each iron atom bonded to three CO ligands and each platinum atom bonded to a CO and a PPh₃ group. The hydrido-ligands are considered to bridge the two longer Fe–Pt edges. The X-ray studies allow an understanding of the ¹H and ³¹P n.m.r. data for the two Fe₂Pt₂ species, both of which undergo dynamic behaviour in solution. Reactions of the compound [Pt(C₂H₄)₂(PPh₃)] or [Pt(cod)(C₈H₁₃)][BF₄](cod = cyclo-octa-1,5-diene) with the salt [NEt₃H][Fe₃(µ-H)(µ-CO)(CO)₁₀] afford the compounds [NEt₃H][Fe₃Pt(µ-H)(µ-CO)(CO)₁₀(PPh₃)] and [Fe₂Pt(CO)₈(cod)], respectively. The latter was studied by X-ray crystallography; crystals are orthorhombic, space group P2₁2₁, Z= 4, in a unit cell of dimensions a= 12.321 (11), b= 9.442(7), and c= 15.707(16)Å. The structure has been refined to R 0.050 (R′ 0.050) for 1 637 independent reflections to 2θ⩽ 55° at 200 K. The molecule consists of a triangle of metal atoms [Fe–Pt 2.561 (3) and 2.553(3); Fe–Fe 2.704 (4)Å]; each iron atom carries four terminally bound CO ligands, and the platinum atom is η⁴ bonded to the cod group.