Lithiation of 1,2-dicarba-closo-dodecaborane(12) (1) followed by insertion of selenium into both C-Li bonds leads to the 1,2-diselenolato-1,2-dicarba-closo-dodecaborane(12) dianion (3), which is converted by oxidative coupling into the cyclic eight-membered bis(diselane) 4 with annellated carborane moieties. Oxidative addition of 4 to ethenebis(triphenylphosphane)platinum(0) gives the bis(triphenylphosphane)platinum(II) complex 7, which contains a chelating 1,2-diselenol-

9) moieties between the selenium atoms were determined by X-ray analyses. In the case of the chlorosilanes, the analogous five-member ring containing the SiPh 2 unit (4) could be identified in mixtures. The expected reaction was accompanied by rearrangement leading to formation of another five-member ring 6 containing the Ph 2 Si-Se-Se moiety. Oxidative addition of the five-member heterocycles containing tin (7, 9) to ethene-bis(triphenylphosphane)platinum(0) gave at low temperature the bis(triphenylphosphane)platinum(II) complexes 12 and 13, where the Pt(PPh 3 ) 2 fragment had been inserted into one of the Sn-Se bonds. Extensive decomposition of these complexes was observed above −20 • C. The proposed solution-state structures of the new compounds are supported by multinuclear magnetic resonance data ( 1 H, 11 B, 13 C, 29 Si, 31 P, 77 Se, 119 Sn and 195 Pt NMR). To a solution of ethene-bis(triphenylphosphane)platinum(0) (0.14 g, 0.19 mmol) in CD 2 Cl 2 (0.5 ml) at −78 • C was added a solution of 7 (0.086 g, 0.19 mmol) in CD 2 Cl 2 (0.5 ml). An orange-red reaction solution was obtained and studied immediately by 31 P NMR spectroscopy. At −80 • C, the

The reaction of the 1,2-diselenido-1,2-dicarba-closo-dodecaborane dianion (1) with dichloro(phenyl)phosphane affords the 1,3,2-diselenaphospholane (2) containing an anellated dicarbacloso-docecaborane(12) unit. The phospholane 2 was oxidised by reactions with the elements to the sulfide 3 and the selenide 4, and partial hydrolysis gave a selenophosphonic acid derivative 5 along with the bis(diselane) 6 and decomposition. The reaction of 2 with (ethene)bis(triphenylphosphane)platinum(0) displaces ethene and is accompanied by oxidative addition and rearrangement into the 851 bis(triphenylphosphane)platinum(II) complex 9, in which the chelating unit is linked to platinum via Pt-Se and Pt-P(Se) bonds, a rare example of a metallophosphane selenide. The molecular structures of 2 and 3 were determined by X-ray analysis. The solution-state structures of the new compounds follow from consistent multinuclear magnetic resonance data ( 1 H, 11 B, 13 C, 31 P, 77 Se, 195 Pt NMR).

The origin of broadening of 13C(carborane) NMR signals of 1,2‐, 1,7‐ and 1,12‐dicarba‐closo‐dodecaboranes(12) and several diphenylsilyl derivatives has been examined in detail and could be traced only partially to unresolved 13C–11B spin‐spin coupling. Other contributions to the line widths arise from 13C–1H dipole‐dipole interactions and, in particular, from isotope‐induced chemical shifts 1Δ10/11B(13C), observed here for carboranes for the first time. In the case of 1‐diphenylsilyl‐1,2‐dicarba‐closo‐dodecaborane(12), the coupling constant 1J(13C,13C) = 9.3 Hz was measured in natural abundance of 13C. The small value of this coupling constant and its negative sign is predicted by calculations based on optimised structures [B3LYP/6‐311+G(d,p) level of theory] of the parent carboranes and 1‐silyl‐1,2‐dicarba‐closo‐dodecaborane(12) as a model compound [calcd. 1J(13C,13C) = –10.5 Hz]. Calculated coupling constants 1J(13C,11B) are small (<7 Hz), in contrast to published assumptions, and of either sign, whereas 1J(11B,11B) are all positive and range up to 15 Hz.

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