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Synthesis and structural elucidation of various electron precise group 5 dimetallaheteroboranes have been described. Room temperature reaction of [Cp 2 VCl 2 ] with Li[BH 3 (EPh)], generated from the treatment of LiBH 4 ·THF and Ph 2 E 2 (E = S or Se), for 1 h in toluene, followed by thermolysis, led to the formation of bimetallic complexes [{CpV(μ-EPh)} 2 {μ-η 2 :η 2 -BH 3 E}], 1 and 2 (1: E = S and 2: E = Se), and [{CpV(μ-SePh)} 2 {μ-η 2 :η 2 -BH(OC 4 H 8 )Se}], 3. One of the striking features of these compounds is that they represent a rare class of distorted tetrahedral clusters having bridging hydrogens. Evaluating the skeletal electron pairs and bonding types, compounds 1, 2, and 3 may be considered as isoelectronic with our earlier reported [(CpV) 2 (B 2 H 6 ) 2 ]. In an attempt to synthesize the Nb analogues of 1-3, room temperature reactions of [CpNbCl 4 ] and Li[BH 3 (EPh)] (E = S or Se) were carried out that afforded compounds [{CpNb(μ-EPh)} 2 {μ-η 2 :η 2 -B 2 H 4 E}], 4 and 5 (4: E = S and 5: E = Se). The solid-state X-ray structures of both 4 and 5 exemplify electronically saturated [M 2 B 3 ] systems, and their geometries are analogous to that of [(Cp*MoCl) 2 B 3 H 7 ]. For the extension of this work, reaction of [Cp*TaCl 4 ] (Cp* = η 5 -C 5 Me 5 ) with Li[BH 3 (SePh)] was carried out that yielded a tantalaselenaborane cluster [(Cp*Ta) 2 (μ-Se)B 3 H 6 Se(C 6 H 5 )] (6). All the new compounds have been characterized using 1 H, 11 B{ 1 H}, 13 C{ 1 H} NMR, UV-vis absorption, and IR spectroscopy, mass spectrometry, and X-ray diffraction studies.

Dinuclear salen compounds of zirconium and hafnium are efficient initiators for the solvent-free ring-opening polymerization of cyclic ester monomers and lactides. There is a correlation between the theoretical and experimental number-average molecular weights (M(n)'s) in these polymerizations. Polymerization of β-butyrolactone gives poly(3-hydroxybutyrate) with a good M(n) and molecular weight distribution.

Pyrolysis of (eta(5)-C(5)Me(5)WH(3))B(4)H(8), 1, in the presence of excess BHCl(2) x SMe(2) in toluene at 100 degrees C led to the isolation of (eta(5)-C(5)Me(5)W)(2)B(5)H(9), 2, and B-Cl inserted (eta(5)-C(5)Me(5)W)(2)B(5)H(8)Cl, 3, and (eta(5)-C(5)Me(5)W)(2)B(5)H(7)Cl(2), 4-7 (four isomers). All the chlorinated tungstaboranes were isolated as red and air and moisture sensitive solids. These new compounds have been characterized in solution by (1)H, (11)B, (13)C NMR, and the structural types were unequivocally established by crystallographic analysis of compounds 3, 4, and 7. Density functional theory (DFT) calculations were carried out on the model molecules of 3-7 to elucidate the actual electronic structures of these chlorinated species. On grounds of DFT calculations we demonstrated the role of transition metals, bridging hydrogens, and the effect of electrophilic substitution of hydrogens at B-H vertices of metallaborane structures.