Bidentate P-ligands

The effect of the bite angle has been reviewed.243,244 The 103Rh chemical shifts of a series of hydridorhodiumbis(carbonyl)diphosphine compounds containing chelating bidentate P-ligands have been obtained by inverse HMQC detection sequences.245... 

The dirhenium complexes in System 5 exhibit a peculiar dependence on change from bidentate P ligands to bidentate As ligands. In all cases the As ligands seem to stabilize preferentially the highest oxidation state for the two most extreme electron transfer reactions (the second reduction and the second oxidation for the neutral complexes, third reduction and first oxidation for the positively charged ones), whereas the opposite is the case for the two intermediate electron transfers. 

A novel bidentate P-ligand was prepared from the 3-diphenylphosphinoxido-l-phenyl-tetrahydrophosphinine oxide (54, Z = Ph) by double deoxygenation. Reaction of the bisphosphine (64) so obtained with dichlorodibenzonitrileplatinum (II) afforded cis chelate complex 65 (Scheme 29) [39],... 

Van der Eycken et al. elaborated the four-step synthesis of 2,5-diphenylphos-phinoxidonorbornane. According to this, 2,5-norbornadione is transformed to the bis(phosphinoxido)norbornadiene via the bis(enolate) and the unsaturations are removed by catalytic hydrogenation (Scheme 21). The racemic bis(phosphinoxido)-norbornane was resolved to give the precursor of bidental P-ligand (IS, 5S)-DIPHONANE. 

The twist-boat conformation was sensitive to substitution effects and the 3-P(0)Ph2-substituted cyclic phosphine oxides proved to be excellent precursors of bidentate P-ligands. 

Some compounds with a bidentate P ligand bridging two Ru atoms are given in Table 2. The ligands are usually strictly spectator ligands taking the place of two carbonyl ligands. 

The next efforts were directed to obtain precursors of bidentate P-ligands. In connection with the synthesis of the precursor of LuPhos and its Pt complex [59], the addition of diphenylphosphine oxide to l-phenyl-2-phospholene 1-oxide (40) was studied under MW conditions. The MW-assisted addition of other >P(0)H species was also investigated. It was found that in most of the cases, the reaction was not selective xmder MW irradiation (Scheme 14). The traditional activation of the >P(0)H species by MesAl followed by the addition of the anion so formed led to "clean" reactions [60]. 

The S3mthesis of another kind of bidentate P-ligand was based on the addition of >P(0)H species at the end of the a,p-double bond of 1,2-dihydrophosphinine oxides (42). As the double bond was not too reactive, the activation of the >P(0)H reagent by MesAl was necessary prior to the addition to obtain the 3-phosphono- ((R0)2P(0)-), 3-phosphinoyl- (Ph2P(0)-), and other related ((EtO)PhP(0)-)l,2,3,6-tetrahydrophosphinine oxides (43) (Scheme 15) [61,62]. Under MW irradiation, there was no reaction. The 3-substituted-l,2,3,6-tetrahydrophosphinine oxides (43) were converted to the fully saturated 1,2,3,4,5,6-hexahydrophosphinine oxides (44) by catalytic hydrogenation (Scheme 15) [63,64]. 

Bis(phosphinoylmethyl)ainines (58) are useful precursors of bidentate P-ligands (59) obtained after double deoxy-genabon by silanes, e.g., trichlorosilane that could be used for the synthesis of ring platinum complexes (60) by reaction with dichlorodibenzonitrile platinum (Scheme 22) [75-78]. Ring Pt complexes are special heterocycles that may be regarded potential catalysts in homogeneous catalysis. 

The double Kabachnik-Fields (phospha-Mannich) reaction of primary amines, two equivalents of paraformaldehyde and the same amount of diphenylphosphine oxide gave bis(diphenylphosphinoylmethyl)amines that were precursors of bidentate P-ligands after double deojq genation... 

First example of p(/), /) )-C104 as a bidentate bridging ligand (to Ag ) chelating /) -C104 identified in 197 4... 

Other species tested in situ are chelating bis-imidazolium structures with phe-nylene spacers [48], and bidentate C-P ligands [49] that achieved, in the case of triarylphosphine-imidazolium salts, very good yields for a wide variety of substituted aryl bromides (Scheme 6.11) [50]. 

Barnard, P.J., Baker, M.V., Bemers-Price, S.J., Skelton, B.W. and White, A.H. (2004) Dinudear gold(I) complexes of bridging bidentate carbene ligands Synthesis, structure and spectroscopic characterisation. Dolton Transactions, 1038-1047. 

A combination of P- and N- donors is another useful approach to potentially reactive (and cataly-tically active) Ni species. Similar to O- donors, N is a hard donor capable of stabilizing metal ions in higher oxidation states, whereas the soft donor P is best suited to stabilize medium or low oxidation states. A neutral bidentate P,N ligand combining a hard dimethylamino and a soft phosphine donor in /V,/V -dimethyl-2-(diphenylphosphino)aniline (241) affords the neutral trigonal bipyramidal and the... 

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