Group 4 metallacarboranes of constrained geometries derived from B (cage)- and C (cage)-silylamido-substituted carborane ligands: a synthetic and structural investigation

Abstract

The reactions of RNHSi(Me) 2Cl ( 1, R= t-Bu; 2, R=2,6-(Me 2CH) 2C 6H 3) with the carborane ligands, nido-1-Na(C 4H 8O)-2,3-(SiMe 3) 2-2,3-C 2B 4H 5 ( 3) and Li[ closo-1-R′-1,2-C 2B 10H 10] ( 4), produced two kinds of neutral ligand precursors, nido-5-[Si(Me) 2N(H)R]-2,3-(SiMe 3) 2-2,3-C 2B 4H 5, ( 5, R= t-Bu) and closo-1-R′-2-[Si(Me) 2N(H)R]-1,2-C 2B 10H 10 ( 6, R= t-Bu, R′=Ph; 7, R=2,6-(Me 2CH) 2C 6H 3, R′=H), in 85, 92, and 95% yields, respectively. Treatment of closo-2-[Si(Me) 2NH(2,6-(Me 2CH) 2C 6H 3)]-1,2-C 2B 10H 11 ( 7) with three equivalents of freshly cut sodium metal in the presence of naphthalene produced the corresponding cage-opened sodium salt of the “carbons apart” carborane trianion, [ nido-3-{Si(Me) 2N(2,6-(Me 2CH) 2C 6H 3)}-1,3-C 2B 10H 11] 3− ( 8) in almost quantitative yield. The reaction of the trianion, 8, with anhydrous MCl 4 (M=Ti and Zr) in 1:1 molar ratio in dry tetrahydrofuran (THF) at −78 °C, resulted in the formation of the corresponding half-sandwich neutral d 0-metallacarborane, closo-1-M[(Cl)(THF) n ]-2-[1′-η 1σ-N(2,6-(Me 2CH) 2C 6H 3)(Me) 2Si]-2,4-η 6-C 2B 10H 11 (M=Ti ( 9), n=0; M=Zr ( 10), n=1) in 47 and 36% yields, respectively. All compounds were characterized by elemental analysis, 1H-, 11B-, and 13C-NMR spectra and IR spectra. The carborane ligand, 7, was also characterized by single crystal X-ray diffraction. Compound 7 crystallizes in the monoclinic space group P2 1/ c with a=8.2357(19) Å, b=28.686(7) Å, c=9.921(2) Å; β=93.482(4)°; V=2339.5(9) Å 3, and Z=4. The final refinements of 7 converged at R=0.0736; wR=0.1494; GOF=1.372 for observed reflections.