Superbasic bridgehead diphosphines: the effects of strain and intrabridgehead P  · · ·  P bonding on phosphine basicity

Abstract

The basicity order in acetonitrile for a series of phosphines is: 1,5-diphosphabicyclo [3.3.3]undecane 1 (pK a for the protonated ion ~17.9) < 1, 6-diphosphabicyclo[4.3.3]dodecane 2 (pK a ~22.5) < 1,6-diphosphabicyclo[4.4.3]tridecane 3 (pK a 27.8). The latter is therefore comparable to Schwesinger's P 1 -t-Bu base but still significantly weaker than Verkade's proazaphosphatrane bases. The pK a for the protonated ion of 1,6-diphosphabicyclo[4.4.4]tetradecane 4 could not be determined due to rearrangement probably caused by preferred deprotonation at α-carbon. However, the X-ray structure of 4HؒPF 6 ( 1 J PP 178 Hz) shows an in,out structure with a P ؒ ؒ ؒ P distance of 2.58 Å, indicative of significant bonding. Diphosphines 2 and 3 protonate to give in,out-2H ϩ ( 1 J PP 251 Hz) and in,out-3H ϩ ( 1 J PP 253 Hz), but 1H ϩ shows no P-P coupling and is believed to be out,out. Proton affinities (PA) for the bridgehead diphosphines have been calculated at the B3LYP/6-31G* level: 1, 1001, 2, 1040, 3, 1085, and 4, 1105 kJ mol Ϫ1 and are compared with PA[(t-Bu) 3 P] = 1028 kJ mol Ϫ1 . All the bridgehead diphosphines are strongly flattened and the question of how much this may contribute to their enhanced basicity, in addition to the effect of intrabridgehead bonding, is discussed.

Sequestration of CO2by Phosphatrane Molecules

“…[13][14][15][16][17][18][19][20] Phosphatrane molecules are a tricyclic cage-like heterocycles which present the possibility to have a transannular dative bond with a nitrogen or another heteroatom. The pioneer synthetic work in the groups of Alder and Verkade [21][22][23][24][25][26][27][28][29] showed that depending of the size, substituents and environment they can adopt out:out and/or in:out conformations. In previous works, we have demonstrated that the change of the conformation can have profound implications in the nucleophilic character of the terminal phosphorous atom, and thus, the equilibrium between out:out and in:out conformation can be tuned through the interaction with Lewis acids.…”

Bridged Dinuclear Tripodal Tris(amido)phosphane Complexes of Titanium and Zirconium as Diligating Building Blocks for Organometallic Polymers

“…The target bis-(phosphane) building blocks for such an approach are shown in Scheme 1, and feature a pair of metal-bearing tripodal tris(amido)phosphane ligands, as well as a bridge between the metal centers labeled M. The addition of suitable late-transition-metal fragments capable of bonding to two phosphane moieties, labeled MЈL n in Scheme 1, should provide a facile route to transition-metal-containing oligomers and polymers. Although there are a plethora of examples of bis(phosphanes) used as bridging ligands, [22][23][24] as well as flexible ligands incorporating hard and soft donors that have been utilized as building blocks for bimetallic and polynuclear early-late transition-metal clusters, [25,26] the complexes we propose here could provide rare examples of linear bis(phosphane) building blocks, [27][28][29][30][31][32] where throughspace interactions provide the potential for extended interactions. In this paper, we test the synthetic feasibility of preparing such building blocks using the diamagnetic early transition metals zirconium and titanium, with the goal of introducing redox active and paramagnetic metal-bridge fragments in future endeavours.…”

A Nontemplated Route to Macrocyclic Dibridgehead Diphosphorus Compounds: Crystallographic Characterization of a “Crossed‐Chain” Variant of in/out Stereoisomers

“…Reactions with excesses of appropriate nucleophiles then afforded the demetalated diphosphines in good yields . Interestingly, the “largest” such diphosphine previously synthesized consisted of one (CH 2 ) 3 and two (CH 2 ) 4 bridges …”

“…[2][3][4][5] Interestingly,t he "largest" such diphosphinep reviously synthesized consisted of one (CH 2 ) 3 and two (CH 2 ) 4 bridges. [6] Macrobicyclic dibridgehead diphosphines, such as 1c,e,a re capable of homeomorphism, [7] ad ynamic process that was defined 50 years ago, butr emains unfamiliar to many chemists. As exemplified with 1c and adducts thereof in Scheme 2, one bridge is threaded through the other two, which effectively turns the molecules inside out.…”