Metallaheteroborane chemistry. Part 3. Synthesis of [2,2-(PR3)2-1,2-TePtB10H10](R3= Et3, Bun3, or Me2Ph), their characterisation by nuclear magnetic resonance spectroscopy, and the crystal and molecular structure of [2,2-(PEt3)2-1,2-TePtB10H10]

Abstract

Reaction of [Pt(PR₃)₂Cl₂](R₃= Et₃, Buⁿ₃, or Me₂Ph) with the [7-TeB₁₀H₁₁]^– anion in refluxing tetrahydrofuran affords the compounds [2,2-(PR₃)₂-1,2-TePtB₁₀H₁₀][R₃= Et₃(1), Buⁿ₃(2) or Me₂Ph (3)] as the major products. An X-ray diffraction study of (1)(recrystallised from CH₂Cl₂) shows the crystals to be monoclinic, space group Cc with four molecules in a unit cell of dimensions a= 10.387(2), b= 17.227(4), c= 14.447(3)Å, and β= 106.83(2)°. The final R factor was 0.020 for 2 601 observed reflections. Principal interatomic distances are Pt–Te 2.704(1), Pt–P 2.320(2) and 2.341(2), Pt–B 2.248(7)–2.295(9), Te–B 2.291(8)–2.404(8)Å. The compounds, together with the [TeB₁₀H₁₁]^– precursor, have been examined by n.m.r. spectroscopy, and several interesting features are noted. Relative sign information for the various ⁿJ(¹⁹⁵Pt–¹H) couplings to the heteroborane cluster protons is apparent from two-dimensional [¹H–¹H]-COSY experiments, and variable-temperature ¹H-{³¹P} spectroscopy on compound (3) reveals ΔG₃₂₈‡= 62 kJ mol^–1 for the rotational metal-to-heteroborane bonding fluxionality.