Diphenylphosphidoboratabenzene:  An Anionic Analogue of Triphenylphosphine

Abstract

Stimulated by its relationship to the ubiquitous triphenylphosphine ligand (1), 1 we have prepared 2 and begun to explore the coordination chemistry of the diphenylphosphidoboratabenzene anion (DPB; 2). DPB may be viewed as a negatively charged, essentially isosteric, variant of PPh 3 ; within this context, comparative studies of PPh 3 and DPB complexes, both for a given metal and for metals which are adjacent in the periodic table, could lead to useful new insights into reactivity. 3 In this communication, we report the first stage of our investigation into the chemistry of DPB, specifically, synthetic and structural work which establishes the viability of DPB as a ligand for an array of transition metals.A wide range of DPB adducts can be generated through treatment of transition metal halides with potassium diphenylphosphidoboratabenzene (K-DPB). For example, reaction of Cp 2 ZrHCl with K-DPB in the presence of PMe 3 leads to displacement of the chloride ligand and formation of Cp 2 ZrH-(DPB)(PMe 3 ) (3; eq 1). A single-crystal X-ray diffraction study of this complex ( Figure 1a; Table 1a) 4 reveals a structure very similar to that found for Cp 2 ZrH(SiPh 3 )(PMe 3 ). 5 The P-C bonds of the DPB ligand are ∼0.12 Å shorter than the P-B bond, and the ligand adopts a slightly distorted tetrahedral geometry.We have also established that the iodide of CpFe(CO) 2 I is readily substituted by DPB, producing CpFe(CO) 2 (DPB) (4, eq 2). The X-ray crystal structure of 4 ( Figure 1b; Table 1b) 6 displays a three-legged piano-stool geometry typical of CpFeL 2 X complexes, with a nearly staggered conformation about the Fe-P bond (dihedral angle [Cp centroid-Fe(1)-P(1)-C(31)]) -168°). 7 As in the case of zirconium complex 3, the P-C bonds of the DPB ligand of 4 are shorter than the P-B bond (by ∼0.13 Å).[CpFe(CO) 2 (PPh 3 )] + and CpFe(CO) 2 (PPh 2 ) are isoelectronic with complex 4. 8,9 Comparison of the C-O stretching frequencies (Table 2) suggests that the iron atom of [CpFe(CO) 2 -(PPh 3 )] + is the least electron-rich and that of CpFe(CO) 2 (PPh 2 ) is the most electron-rich. It is important to note that the diphenylphosphido group is unique among the three phosphorus ligands in that it bears a "lone pair" which can contribute electron density to the metal. The IR data as well as the Fe-(1) For a review of phosphine complexes of transition metals, see: Dias, P. B.; de Piedade, M. E. M.; Simoes, J. A. M. Coord. Chem. ReV. 1994, 135, 737-807. (2) Qiao, S.; Hoic, D. A.; Fu, G. C. J. Am. Chem. Soc. 1996, 118, 6329-6330.(3) This general approach has proved to be extremely interesting in early transition metal metallocene chemistry. For examples and leading references, see: (a) Crowther, D. J.; Baenziger, N. C.; Jordan, R. F. Data for compound 3: A wheat-colored plate (0.08 × 0.09 × 0.39 mm; grown from toluene/reaction-mixture at -35°C for three weeks) was mounted with a glass fiber on a Siemens SMART/CCD three circle diffractometer ( fixed at 54.78°). Data collection was done at -120°C using Mo KR radiation. The crystal was ...

Chemistry of Phosphine–Borane Adducts at Platinum Centers: Synthesis and Reactivity of PtII Complexes with Phosphinoborane Ligands

“…In addition, transition-metal complexes containing a secondary phosphidoboratabenzene ligand have been synthesized and characterized by X-ray crystallography; namely, [Fe(h . [30] However, routes to these complexes all require a nucleophilic substitution step, rather than oxidative addition of the phosphine ± borane adduct itself. Recently, the reaction of a transition-metal-complexed phosphine [ 2 ], in which insertion of the Pt 0 center into the PÀH bond of the phosphine has occurred.…”

Broadening the Scope of Ancillary Phosphane‐Type Ligands: A Systematic Comparison of PR3, PR2BH3–, and SiR3– and Their Chalcogen Derivatives

“…[29] In a 1996 paper, Fu and co-workers described diphenylphosphidoboratabenzene, PPh 2 (BC 5 H 5 ) -, as the anionic analog of triphenylphosphane and investigated its coordination chemistry. [30] www.eurjic.org…”

“…[54][55][56][57] The σ-donor properties of the phosphanyl borohydride 2a (Figure 2) towards selected main group Lewis acids have already been explored. [58] It was found that 2a forms stronger Lewis acid-base adducts than the related phosphane PPh 2 Me (1 [27][28][29][30] The complex [FpPPh 2 BH 3 ] was prepared from FpPPh 2 and BH 3 ·thf and was characterized spectroscopically. [59] The few examples of Fp-phosphane chalcogenide complexes with trialkyl-and triarylphosphane chalcogenides EPR 3 (R = iPr, tBu, Ph; E = O, S, Se) were prepared by reaction with [Fp(thf)]BF 4 and characterized spectroscopically [60] and, in part, by cyclic voltammetry.…”

Phosphanylborohydrides: First Assessment of the Relative Lewis Basicities of [BH3PPh2]–, CH3PPh2, and HPPh2

“…[12] Stimulated by their investigations, our group embarked on a systematic study of the ligand properties of anionic phosphanylborohydrides [BH 3 PRRЈ] -in comparison to their neutral isoelectronic and isostructural methyl analogues CH 3 PRRЈ. For a start, we are focusing on compounds in which the phosphorus atom is exclusively engaged in σ bonds.…”