Synthesis and structural characterization of binuclear titanium(IV) and tantalum(V) cyclopentadienyl complexes containing bridging phosphinate ligands

Abstract

The reaction of Ph2P(O)(OSiMe3) with [(η5-C5H5)TiCl3] or [(η5-C5Me5)TaCl4] in dichloromethane yields the complexes [{(η5-C5H5)TiCl2(µ-Ph2PO2)}2] (1) or [{(η5-C5Me5)TaCl3(µ-Ph2PO2)}2] (2), respectively. Structural analysis of 1 and 2 by single-crystal X-ray diffraction revealed the presence of eight-membered metallacycles consisting of bridging–bidentate diphenylphosphinate groups between two metal centers.Key words: inorganic rings, phosphinate complexes, tantalum, titanium.

Cross-dehydrocoupling: A Novel Synthetic Route to P–B–P–B Chains

“…Partial H/Cl exchange between the terminal BH 3 group and a chlorine atom of the catalyst [{Rh(μ-Cl)(1,5-cod)} 2 ] was observed in the single-crystal X-ray diffraction measurements of 3a and 3b [H/Cl occupancy = 0.741(6)/0.259(6) for 3a and 0.871(3)/0.129(3) for 3b]. H/Cl exchange in the dehydrocoupling reaction was also reported by Manners et al 47 Molecular structures of 3a and 3b are given in the SI (Figure S3). Compounds 3a and 3b were further characterized by 1 H, 13 C{ 1 H}, 31 P{ 1 H}, and 11 B{ 1 H} NMR spectroscopy, elemental analysis, and mass spectrometry.…”

Effect of the Phosphine Steric and Electronic Profile on the Rh-Promoted Dehydrocoupling of Phosphine–Boranes

“…Further insight comes from the observations that for R = t Bu the barrier to dehydrocoupling is higher (70 °C versus 25 °C for reaction), P−H activation appears also to be a higher energy process, different intermediates (A and E) are observed, and the turnover limiting process in catalysis is now suggested to be the P−H activation/dehydrocoupling steps. Prior work has demonstrated a similar difference in relative rates of dehydrocoupling of secondary H 3 B•PR 2 H [R = p-(CF 3 )C 6 H 4 , Ph, t Bu, i Bu] and primary H 3 B•PRH 2 [R = Ph, t Bu, i Bu] phosphine−boranes using the [Rh(COD) 2 ][OTf] catalyst, and this was suggested to be due to a combination of steric and electronic (relative P−H bond strengths) factors, 21,32,33 although the mechanism of dehydrocoupling of phosphine− boranes using this catalyst is currently not known. 20,25,30 Interestingly, the related dehydrogenation of aryl amine− boranes shows that the activity of the N−H bond is such that spontaneous dehydrocoupling occurs in the absence of catalyst, with electron-withdrawing aryl groups [p-(CF 3 )C 6 H 4 ] undergoing faster reaction than electron-donating [p-(OMe)C 6 H 4 ].…”

Mononuclear Schiff Base Boron Halides: Synthesis, Characterization, and Dealkylation of Trimethyl Phosphate

“…Molecular phosphates and phosphonates are interesting because of their possible use as precursors to solid-state materials. − Examples of monomeric main group or transition metal chelate compounds with terminal phosphinates are rare. Previously reported metal phosphinate compounds of Ti, , Zr, Ta, Sn, , Pb, Al, , Ga, , and In 52 contained bridging phosphinate groups, and almost all of the compounds were di- or polynuclear. A unique example of a mononuclear metal chelate phosphinate compound is Sn(CH 2 Ph) 2 [O 2 P(C 6 H 11 ) 2 ] 2 [HO 2 P(C 6 H 11 ) 2 ] 2 (Figure ) .…”

“…For example, in [(η 5 -Cp)TiCl 2 (µ-Ph 2 PO 2 ) 2 ] the 31 P shift was 34.5 ppm. 46 The IR for 14 showed strong ν B-N absorption at 1014 cm -1 , ν (CdN) at 1640 cm -1 , and ν (PdO) at 1212 cm -1 . The MS (EI, positive) showed a molecular ion peak in 15% abundance and a M + -PhPO 2 peak in 45% abundance.…”

“…The chemical shift is close to some other phosphinate compounds. For example, in [(η 5 -Cp)TiCl 2 (μ-Ph 2 PO 2 ) 2 ] the 31 P shift was 34.5 ppm . The IR for 14 showed strong ν B - N absorption at 1014 cm -1 , ν (C  N) at 1640 cm -1 , and ν (P  O) at 1212 cm -1 .…”