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]

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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.

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