Synthesis, molecular structure, and nuclear magnetic resonance investigation of the platinanonaborane and diplatinadecaborane cluster compounds, [4,4-(PMe2Ph)2-arachno-4-PtB8H12] and [6,6,9,9-(PMe2-Ph)4-arachno-6,9-Pt2B8H10]

Abstract

The reaction of cis-[PtCl₂(PMe₂Ph)₂] with an excess of [B₉H₁₄]^– gives 4,4-bis(dimethylphenylphosphine)-arachno-4-platinanonaborane, [4,4-(PMe₂Ph)₂-4-PtB₈H₁₂], (I), in high yield. The pale yellow crystals are monoclinic, space group C2/c, with a= 1.977 1(8), b= 1.302 5(4), c= 1.977 3(4) nm, β= 110.99(3)°, Z= 8, and the molecular structure is that of a nine-vertex arachno-platinanonaborane in which the B₈ unit shows trihapto-bonding to the metal centre. The compound is also formed in lower yield from several other polyhedral borane derivatives. The 14-vertex bis(dimethylphenylphosphine)bis-µ-(2–4-η-nido-hexaboranyl)-diplatinum(Pt–Pt), [Pt₂(B₆H₉)₂(PMe₂Ph)₂], is also formed in moderate yield from the [B₉H₁₄]^– reaction, and this offers the most convenient route yet established for its preparation. Treatment of (I) with KH followed by cis-[PtCl₂(PMe₂Ph)₂] gives the very stable diplatinum compound 6,6,9,9-tetrakis(dimethylphenylphosphine)-arachno-6,9-diplatina-decaborane, [6,6,9,9-(PMe₂Ph)₄-6,9-Pt₂B₈H₁₀], (II). The colourless crystals are monoclinic, space group C2/c, with a= 1.376 2(3), b= 1.510 5(4), c= 1.921 0(3) nm, β= 92.59(2)°, and Z= 4; the molecular structure is that of an arachno-diplatina-decaborane which features a bis(trihapto) B₈ unit. It is topologically similar to, but not identical with, the arachno-decaborane anion [B₁₀H₁₄]^2–. The ¹H, ¹¹B, ³¹P, and ¹⁹⁵Pt n.m.r. behaviour of both title compounds has been investigated in detail using both single and double resonance techniques, and a number of important structural correlations emerge.