Synthesis, reactions, and nuclear magnetic resonance studies of some substituted arachno-decaborane and arachno-nonaborane derivatives, and the isolation of novel polyhedral diplatinaboranes. Crystal and molecular structure of [Pt2(PMe2Ph)2(η3-B2H5)(η3-B6H9)]

Abstract

Reaction of nido-2-XB₁₀H₁₃(X = Cl, Br, or I) with SMe₂ afforded almost quantitative yields of arachno-2-X-6,9-(SMe₂)₂-B₁₀H₁₁ which, when heated under reflux with ROH (R = Me or Et), gave moderate yields of arachno-1-X-4-(SMe₂)-B₉H₁₂ together with the corresponding arachno-4-(SMe₂)-7-(OR)-B₉H₁₂. Deprotonation of 1-Cl-4-(SMe₂)-B₉H₁₂ followed by reaction with cis-[PtCl₂(PMe₂Ph)₂] gave [2-Cl-4,4-(PMe₂Ph)₂-arachno-4-PtB₈H₁₁]. Similar treatment of 4-(SMe₂)-7-(OMe)-B₉H₁₂ gave the corresponding compound [8-(OMe)-4,4-(PMe₂Ph)₂-arachno-4-PtB₈H₁₁] together with variable (small) yields of the known [(PMe₂Ph)₂PtB₃H₇] and [conjuncto-Pt₂(PMe₂Ph)₂(B₆H₉)₂], the novel, yellow, air-stable crystalline compound [conjuncto-Pt₂(PMe₂Ph)₂(B₂H₅)(B₆H₉)], and a new, green, air-stable compound tentatively formulated as [closo-(PMe₂Ph)₃Pt₂B₉H₈(OMe)]. Single-crystal X-ray diffraction studies on [conjuncto-Pt₂(PMe₂Ph)₂(B₂H₅)(B₆H₉)], together with its n.m.r. properties, revealed a novel cluster geometry in which the central almost-linear P–Pt–Pt–P unit is co-ordinated by an η³-B₆H₉nido-subcluster and an opposing η³-B₂H₅ moiety. The crystals are monoclinic, space group P2₁, with a= 1 618.3(9), b= 1 330.0(7), c= 592.3(3) pm, β= 93.62(4)°, and Z= 2. Detailed ¹H, ¹¹B, and ³¹P n.m.r. studies of the various halogen- and alkoxy-substituted platinaboranes are presented, and the mechanistic implications of the observed positions of substitution in the products are discussed.