The Taming of Redox‐Labile Phosphidotitanocene Cations

Abstract

Tame d0 phosphidotitanocene cations stabilized with a pendant tertiary phosphane arm are reported. These compounds were obtained by one‐electron oxidation of d1 precursors with [Cp2Fe][BPh4]. The electronic structure of these compounds was studied experimentally (EPR, UV/Vis, and NMR spectroscopy, X‐ray diffraction analysis) and through DFT calculations. The theoretical analysis of the bonding situation by using the electron localization function (ELF) shows the presence of π‐interactions between the phosphido ligand and Ti in the d0 complexes, whereas dπ–pπ repulsion prevents such interactions in the d1 complexes. In addition, CH–π interactions were observed in several complexes, both in solution and in the solid state, between the phosphido ligand and the phosphane arm. The d0 complexes were found to be light sensitive, and decompose through Ti−P bond homolysis to give TiIII species. A naked d0 phosphidotitanocene cation has been trapped by reaction with diphenylacetylene, yielding a Ti/P frustrated Lewis pair (FLP), which was found to be less reactive than a previously reported Zr analog.

A selective route to aryl-triphosphiranes and their titanocene-induced fragmentation

“…This doublet signal shows strong coupling to one 31 P nucleus with a ( 31 P) = 72 MHz and hyperfine coupling to titanium a ( 49/47 Ti) = 22 MHz. The rather large g -value and small hyperfine coupling to Ti indicates a species with a high spin density on phosphorus, in which only one phosphorus is attached to titanium, as a more complex EPR-signal would be expected otherwise 61. In addition, there is an underlying signal stemming from [Cp 2 Ti(btmsa)], which could be fitted to a species with g iso = 1.973 and a ( 1 H) = 32 MHz 62.…”

Reappraising Schmidpeter's bis(iminophosphoranyl)phosphides: coordination to transition metals and bonding analysis

“…Elemental analysis: a satisfactory elemental analysis could not be obtained; carbon was always too low. This problem has been encountered previously with BPh 4 − salts of Ti, see ref. 64 .…”

“…At 2.8125(13) Å it is distinctly superior to the sum of covalent radii for Ti and P, hinting at the possibility of FLP reactivity. 76 However, the reaction mixture of 4a and ferrocene carboxaldehyde (FcCHO) in CD 2 Cl 2 remained unchanged; we had previously observed that FcCHO is one of the most reactive substrates against Ti/P FLPs, 64,75 therefore we did not investigate the FLP behaviour of 4a any further. Instead, we turned our attention to Zr complexes, which generally display enhanced FLP reactivity compared to Ti.…”

“…Instead, we turned our attention to Zr complexes, which generally display enhanced FLP reactivity compared to Ti. 61,64 We synthesized Zr complexes 5 by salt metathesis between ZrCl 4 and ligands 2. Aer workup, complexes 5a and 5b were obtained in 67% and 71% yield respectively (Scheme 5).…”

“…59,60 We surmised that these compounds could offer a unique opportunity to introduce a phosphide ligand in the coordination sphere of group 4 metals (Scheme 4), an area which we have been investigating for some time. [61][62][63][64] We also became interested in comparing their properties to those of TP, with a particular focus on the naturenormal or dative covalent-of P-P bonds, and the possibility to prepare early-late heterobimetallic complexes (by coordination of a late transition metal to the central phosphorus atom). 32,[34][35][36][37][65][66][67][68] Results and discussion…”