No abstract

The first example of a carborane with a catecholborolyl substituent, [1-Bcat-2-Ph-closo-1,2-C2B10H10] (1), has been prepared and characterized and shown to act as the Lewis acid component of an intermolecular frustrated Lewis pair in catalyzing a Michael addition. In combination with B(C6F5)3 the C-carboranylphosphine [1-PPh2-closo-1,2-C2B10H11] (IVa) is found to be comparable with PPh2(C6F5) in its ability to catalyze hydrosilylation, whilst the more strongly basic B-carboranylphosphine [9-PPh2-closo-1,7-C2B10H11] (V) is less effective and the very weakly basic species [μ-2,2′-PPh-{1-(1′-1′,2′-closo-C2B10H10)-1,2-closo-C2B10H10}] (IX) is completely ineffective. Base strengths are rank-ordered via measurement of the 1J 31P-77Se coupling constants of the phosphineselenides [1-SePPh2-closo-1,2-C2B10H11] (2), [9-SePPh2-closo-1,7-C2B10H11] (3), and [SePPh2(C6F5)] (4).

The cyanomethane adduct of NbCI, analyses for NbC14.3CH,CN (1 ). A crystal-structure determination of this species shows that it contains cis octahedral [NbCI,(NCMe),] and a solvent CH,CN molecule. The unique bond lengths are Nb-N 2.220(13) A and Nb-CI 2.328(2), 2.343(6), and 2.349(4) A. The crystals of (1) are orthorhombic with unit-cell dimensions a = 10.437( 11), b = 13.883( 12), c = 9.828(9) A,Z = 4, and space groupPnma. A total of 729 reflections above background have been collected on a diffractometer and refined to R 0.051.When the cyanomethane adducts of NbX, (X = CI or Br) are treated with Sb2S, in cyanomethane, adducts of NbX,S (X = CI or Br) areformed. The products contain [{NbX,S(NCMe),},] in which there is a Nb-S-Nb-S ring. The crystal structures of two compounds, ( 2) and (3), containing the [{NbCI,S(NCMe),),] dimeric unit have been determined. In (2) there are two molecules of occluded CH&N for each dimer while (3) has one. Both'(2) and(3) are triclinic with space group P1, with (2) having a = 9.031 (7),

A series of 28 analogues of the phytotoxic geranylcyclohexentriol (-)-phomentrioloxin A (1) has been synthesized through cross-couplings of various enantiomerically pure haloconduritols or certain deoxygenated derivatives with either terminal alkynes or borylated alkenes. Some of these analogues display modest herbicidal activities, and physiological profiling studies suggest that analogue 4 inhibits photosystem II in isolated thylakoids in vitro.

Three new carboranylphosphines, [1-(1′-closo-1′,7′-C2B10H11)-7-PPh2-closo-1,7-C2B10H10], [1-(1′–7′-PPh2-closo-1′,7′-C2B10H10)-7-PPh2-closo-1,7-C2B10H10], and [1-{PPh-(1′-closo-1′,2′-C2B10H11)}-closo-1,2-C2B10H11], have been prepared, and from a combination of these and literature compounds, eight new carboranylphosphine selenides were subsequently synthesized. The relative basicities of the carboranylphosphines were established by (i) measurement of the 1 J PSe NMR coupling constant of the selenide and (ii) calculation of the proton affinity of the phosphine, in an attempt to establish which of several factors are the most important in controlling the basicity. It is found that the basicity of the carboranylphosphines is significantly influenced by the nature of other substituents on the P atom, the nature of the carborane cage vertex (C or B) to which the P atom is attached, and the charge on the carboranylphosphine. In contrast, the basicity of the carboranylphosphines appears to be relatively insensitive to the nature of other substituents on the carborane cage, the isomeric form of the carborane, and whether the cage is closo or nido (insofar as that does not alter the charge on the cluster). Such information is likely to be of significant importance in optimizing future applications of carboranylphosphines, e.g., as components of frustrated Lewis pairs.