Metallaheteroborane chemistry. Part 5. Synthesis of closo-[2,2-(PR3)2-1,2-SePtB10H10](R3= Et3, Bun3 or Me2Ph) and arachno-[9,9-(PMe2Ph)2-6,9-SePtB8H10] and their characterisation by nuclear magnetic resonance techniques: the crystal and molecular structures of closo-[2,2-(PEt3)2-1,2-SePtB10H10] and

The close compounds [2,2-(PR3)2-1,2-SePtB10H10], where R3= Et3(1) or Bun3(2), have been isolated in low-to-moderate yield from the reaction between cis-[PtCl2(PR3)2] and nido-[7-SeB10H11]– in tetrahydrofuran. Both closo-[2,2-(PMe2Ph)2-1,2-SePtB10H10](3) and arachno-[9,9-(PMe2Ph)2-6,9-SePtB6H10](4) were isolated from the reaction with R3= Me2Ph. N.m.r. spectroscopy confirms the general structures of the compounds, and variable-temperature 1H-{31P} experiments on (3) show the rotational metal-to-heteroborane bonding fluxionality to have ΔG328‡ca. 58 kJ mol–1. An X-ray diffraction study of compound (1) shows the orthorhombic crystals belong to the space group Fdd2, with Z= 16 and cell dimensions a= 55.052(6), b= 17.842(5), and c= 10.259(4)A, R= 0.042 for 2 551 observed reflections. Cage interatomic distances involving Pt or Se are Pt–Se 2.676(2), Pt–B 2.23(2)–2.32(2), and Se–B 2.08(2)–2.20(2)A. Crystals of (4) are orthorhombic, space group P21nm with a= 6.935(1),b= 10.048(2), and c= 17.413(2)A, R= 0.022 for 1 375 observed reflections. Interatomic distances include Pt–B 2.147(10)–2.230(7) and Se–B 2.062(15)–2.113(8)A. Both the X-ray crystallographic and n.m.r. results for (4) indicate this compound belongs to the arachno class. As a model for (4), the bonding of the PtP2 unit to the heteroborane SB8H10 ligand has been analysed in a frontier-orbital approach.