Synthesis, Structures and Spectroscopic Properties of 1 : 1 Complexes of Gold(I) Halides with Trimesitylphosphine

Abstract

Monomeric two-coordinate gold(I) complexes, [Au(P(mes)₃)X] (P(mes)₃ = tris(2,4,6-trimethylphenyl)phosphine, X = Cl, Br and I), have been prepared and characterized by single-crystal X-ray structure determinations, far-infrared spectroscopy and solution and solid-state CPMAS ³¹ P n.m.r. spectroscopy. X-Ray structure determinations show that crystals obtained from solutions of [NBu₄] [AuX₂] and P(mes)₃ in acetonitrile for X = Cl, Br and I and in dimethylformamide (dmf) for X = Br and I form an isomorphous series of complexes, crystallizing in space group P2₁/c with a ª 8, b ª 22, c ª 13 Å, b ª 98˚ (a form). Crystallization of the chloride from dimethylformamide yields the solvated complex [Au(P(mes)₃)X]·(dmf) in space group P2/a with a 15.224(2), b 10.070(1), c 18.210(4) Å, b 100.42(2)˚. Electrochemical synthesis of the complexes for X = Cl and Br yield two new crystalline phases; the chloride in space group P2₁/c with a 10.249(2), b 8.189(2), c 31.844(3) Å, b 91.68(1)˚ (b form) and the bromide in space group Pbca with a 19.208(4), b 15.586(3), c 16.962(4) Å ( g form). The Au–P bond lengths increase in the order Cl < Br < I with distances c. 0.02–0.03 Å longer than average values for other [Au(PR₃)X] complexes, reflecting steric congestion by the P(mes)₃ ligand. For the unsolvated complexes, the Au–X distances are c. 0.02 Å shorter than average values. For the Cl/dmf solvate, both Au–P and Au–X bond lengths increase. For the a complexes, far-infrared spectra show n(Au ^35,37 Cl) 336, 329 cm ^–1 , n(AuBr) 234 cm ^–1 and n(AuI) 195 cm ^–1 and solid-state ³¹ P CPMAS n.m.r. spectra yield broad peaks with d–3.9 (Cl), –0.6 (Br) and +6.0 I). For the Cl/dmf solvate, n(Au ^35,37 Cl) are 334, 327 cm ^–1 and d is –4.4. Solution ³¹ P n.m.r. spectra in CDCl₃ give sharp single peaks at d –5.0 (Cl), –1.4 (Br) and +5.5 (I) with the similarity of the values with those for the solid-state spectra consistent with similar conformational structures for the [Au(P(mes)₃)X] molecules in the two states.