Diphosphanes derived from phobane and phosphatrioxa-adamantane: similarities, differences and anomalies

Abstract

The homodiphosphanes CgP-PCg (1) and PhobP-PPhob (2) and the heterodiphosphanes CgP-PPhob (3), CgP-PPh(2) (4a), CgP-P(o-Tol)(2) (4b), CgP-PCy(2) (4c), CgP-P(t)Bu(2) (4d), PhobP-PPh(2) (5a), PhobP-P(o-Tol)(2) (5b), PhobP-PCy(2) (5c), PhobP-P(t)Bu(2) (5d) where CgP = 6-phospha-2,4,8-trioxa-1,3,5,7-tetramethyladamant-9-yl and PhobP = 9-phosphabicyclo[3.3.1]nonan-9-yl have been prepared from CgP(BH(3))Li or PhobP(BH(3))Li and the appropriate halophosphine. The formation of 1 is remarkably diastereoselective, with the major isomer (97% of the product) assigned to rac-1. Restricted rotation about the P-P bond of the bulky meso-1 is detected by variable temperature (31)P NMR spectroscopy. Diphosphane 3 reacts with BH(3) to give a mixture of CgP(BH(3))-PPhob and CgP-PPhob(BH(3)) which was unexpected in view of the predicted much greater electron-richness of the PhobP site. Each of the diphosphanes was treated with dimethylacetylene dicarboxylate (DMAD) in order to determine their propensity for diphosphination. The homodiphosphanes 1 and 2 did not react with DMAD. The CgP-containing heterodiphosphanes 4a-d all added to DMAD to generate the corresponding cis alkenes CgPCH(CO(2)Me)=CH(CO(2)Me)PR(2) (6a-d) which have been used in situ to form chelate complexes of the type [MCl(2)(diphos)] (7a-d) where M = Pd or Pt. The PhobP-containing heterodiphosphanes 3 and 5a-d react anomalously with DMAD and do not give the products of diphosphination. The X-ray crystal structures of the diphosphanes 2, 3, 4a, and 5a, the monoxide and dioxide of diphosphane 1, and the platinum chelate complex 7c have been determined and their structures are discussed.

Stable Fluorophosphines: Predicted and Realized Ligands for Catalysis

“…(Similarly, the congestion in CgP À PCg destabilizes this product. [21] ) The energies of all trigonal-bipyramidal R 2 PF 3 isomers and key structural parameters have been included in the Supporting Information. In cognizance of the ligand-map information (Figure 1) and the stability predictions, we decided to focus the catalyst testing on ligands 1-3 and tBu 2 PF.…”

“…[21] ) The energies of all trigonal-bipyramidal R 2 PF 3 isomers and key structural parameters have been included in the Supporting Information. [21] ) The energies of all trigonal-bipyramidal R 2 PF 3 isomers and key structural parameters have been included in the Supporting Information.…”

Mechanism of Phosphine Borane Deprotection with Amines: The Effects of Phosphine, Solvent and Amine on Rate and Efficiency

“…This included those commonly reported for phosphine borane deprotection: diethylamine, [3,10] morpholine, [11] 1,4-diazabicyclo[2.2.2]octane (DABCO, 7), [12] pyrrolidine, [13] triethylamine, [14,16] and N-methylpyrrolidine, [15] as well as diisopropylamine, piperidine, and N,Ndimethylaminopyridine (DMAP), to more broadly explore structure-activity relationships (Figures 2 and 3). …”

“…[5] However, the deprotection step can be more problematic, and a number of alternative strategies to achieve this have been reported. [6][7][8][9] Nonetheless, the most commonly applied procedure is still the use of an amine, [3,[10][11][12][13][14][15] which acts as a competing Lewis base to generate the free phosphine R 3 P, and the corresponding amine-borane (R 3 N·BH 3 ) species. A large variety of amines, stoichiometry, solvent, and reaction temperatures have been reported, with some conditions taking several days to reach acceptable levels of conversion.…”

Stable Fluorophosphines: Predicted and Realized Ligands for Catalysis

“…The source of the stability of t Bu 2 PF with respect to disproportionation lies in the high energy of the very hindered t Bu 2 PP t Bu 2 product. (Similarly, the congestion in CgPPCg destabilizes this product 21…”