Phosphines di

With mono- and di-phosphines the rate laws take different forms,... 

We conclude that only one phosphine attacks a ji-S group of 20. Indeed, the phosphine sulfide product from dmpm is Me2P(S)CH2PMe2, not a bis(sulfide).The other phosphine implicated by Eqs. (32) and (33), whether from a second PR3 or from a di-phosphine, adds as a Lewis base to rhenium. The basis for this is that a pyridine easily replaced one of the phosphines in the mechanism. This proposed mechanism should steer the reaction directly towards formation of 21, but owing to the dilemma posed in point (c), an intermediate likely intervenes. It can partition to the slowly-reacting 21 or to 23, the latter step requiring additional phosphine Scheme 13 shows the postulated mechanism. The dual role for phosphine and the use of Py in its place and the proposal for partitioning are shown in Scheme 14. 

The catalytic activity of cationic rhodium precursors of formula [Rh(diene)(di-phosphine)]+ was also explored by Schrock and Osborn [28]. Halpern and coworkers made very detailed mechanistic studies of olefin hydrogenation by [RhS2(diphos)]+ species (diphos = l,2-bis(diphenylphosphino)ethane S = solvent) [31]. Significant differences have been observed in the reaction of the catalyst precursors [Rh(NBD)(PPh3)2]+ and [Rh(NBD)(diphos)]+ in methanol, as shown in Eqs. (8) and (9) ... 

The redox behaviour of polynuclear clusters has been examined for electrocatalytic properties27. Clusters of the type [Co4(CO)10 JC( 4-PPh)2Lx], where L is a mono-, or di-phosphine having the structures of the type shown ... 

Ru(2-Me-allyl)(di phosphine) a,/)-uDsaturated carboxylic Tetr Asym 2 43 (1991)... 

In the case of the heterobimetallic systems, the few examples known so far are [ClPt(p-dppm)2(p-C=N-Me)Ni(CNMe)]Cl (64), reported by Kubiak and collaborators, which is obtained via a transmetallation of [(CNMe)]Ni (p,-dppm)2(p,-C = N-Me)Ni(CNMe)] with [Pt(dppm)Cl2].80 The other examples are the mixed M-Pt systems 65—74 (M = W, Fe, Mo, Cr) containing a dis-phosphine backbone (dppm or dppa), as described by Knorr and collaborators81 -84 (Fig. 31). These complexes were obtained via substitution of the bridging carbonyl by an isocyanide ligand. 

Numerous other bidentate phosphine ligands have also been tested in this reaction.[40] Interestingly, addition of water to the employed ionic liquids [C8Ciim][BF4] and [C4Ciim][Tf2N] led to increased ees and/or reaction rates compared to common organic solvents when ferrocene-based di-phosphines such as 4 and 5, shown in Figure 3.3, were used. 

Di)phosphines containing chiral backbones equipped with diphenylphosphino-substituents are the most successful and best-investigated chiral ligands in asymmetric homogeneous catalysis. Thus, a variety of chiral water-soluble ligands were prepared by direct sulfonation of these phosphorus ligands under conditions similar to those for the synthesis of achiral sulfonated phosphines. 

P Chemical shifts of some nickel dicarbonyl di(phosphine) complex... 

Recently we have proposed a convenient synthesis of phosphorus analogs of sucrose. Di-chloro-perbenzylated derivative 27 (an intermediate in the synthesis of 22 via route c in Scheme 5), upon reaction with Ph2P anion, provided sucrose di-phosphine 28. However, regardless of the conditions, this compound was always oxidized to phosphine oxide 29. This is rather surprising, since such type of phosphines derived from simple sugars are relatively resistant towards oxidation (Scheme 6). 

Beyond the characteristic chemical shift of the mono and di-phosphine adducts, the INADEQUATE (Incredible Natural Abundance DoublE QUAntum Transfer Experiment) ID NMR of phosphorus-31 (Scheme 3a) has been essential for their attribution (Fig. 2)." ... 

The Matt group has also investigated cavitands as catalysts. For example, cavitand 42 is a catalyst for Heck reactions [120]. Conversion percentages were highest when the cavitand was present in a 1 1 ratio with the Pd ligand. Semeril and Matt have also examined mono- and complexes with ruthenium [121], but the properties of these bulky ligands have to our knowledge not yet been reported. 

Unusual type of P-based cyclophane 154 containing NH,NH-functionalized carbene heterocyclic fragment coordinated to the transition metal was obtained by metal template assisted cyclization reactions of the diphosphine hgand bearing reactive 2-fluoro substiments at phenyl groups on phosphorus atoms and carbene heterocycle in coordination sphere of 153 (Scheme 12.57). Aerial oxidation of the complexes of the cyclophane hgand resulted in the isolation of the free macrocycle as di(phosphine oxide)/imidazolidinium salt [142, 143]. 

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