Diphosphines mixed

An important number of polynuclear pentafluorophenylgold(III) and mixed gold (I)-gold(III) derivatives have been described with the diphosphine 1,2-diphosphmo-benzene, which contains four hydrogen atoms that can be removed and substituted by a metal atom (Scheme 3.5) [220]. 

Diphosphinoamines (X2P-NR-PX2) are examples of a more unusual potentially chelating diphosphine. The dimer Co2(F2PN(CH3)PF2)3(CO)2 has three of these ligands bridging symmetrically between the two tetrahedral Co centers, which also carry a terminal CO group this molecule can undergo reduction with LiEt3BH in THF to form a stable mixed valence (d9—d10) radical anion.163... 

Application of the same dendrimer 31 in the Stille coupling of iodobenzene with tributylvinyltin in DMF (Scheme 10 5mol% catalyst) showed an activity equal to that of the tetraphosphole macrocycle complex (Fu3P)4Pd(OAc)2 (31b 100% conversion after 15 min). In contrast to the monomer, the dendritic catalyst could be recycled, but when recycled it showed a decrease in activity (95% conversion after 15 min). A better performance was achieved with the in situ prepared catalyst 32 by mixing the third-generation diphosphine dendrimer with Pd(OAc)2 (P/Pd ratio = 4/1). An activity similar to that of the monomeric complex (Fu3P)4Pd(OAc)2 was observed (100% conversion after 15 min), even after three consecutive runs. 

A combination of a substitution reaction with a chlorophosphine followed by a hydroboration and boron-zinc exchange allows the preparation of the mixed 1,2-diphosphine 207 in good yield (Scheme 62). ... 

SCHEME 62. Preparation of mixed diphosphines using functionalized zinc organometallics... 

A monophosphine complex is formed when 3 is mixed with three equivalents of a zinc(ii)salphen complex and half an equivalent of Rh(acac)(CO)2 (acac = acetyl acetonate), whereas the assembly based on template 4 and the zinc(n)salphen complexes forms a bis-phosphine rhodium species. In the latter case, the bisphosphine rhodium complex is completely encapsulated by six salphen building blocks. This difference in mono- versus diphosphine ligation to the Rh -center and, to a lesser extent, the difference in electronic features (and thus donating properties of the phosphine) between template ligands 3 and 4, can be used to induce a different catalytic behavior. 

The reaction of an excess of a diphosphine (PP), such as dppe, with [MoOCl2(PR3)3] yields [MoOC1(PP)2]C1 the cation has been isolated as [BF4], [BPh4], [NCS] and [NCSe] salts.109,110 When a stoichiometric (1 1) amount of (PP) is present, the intermediate, mixed phosphine complex [MoOCl2(PP)(PR3)j can be prepared.109 A crystal structure determination of [MoOCl(dppe)2][ZnCl3(OCMe2)] has shown that the cation contains octahedral MoIv.ni... 

Racemic diphosphines may be resolved by using transition metal complexes that contain optically active olefinic substrates (Scheme 11) (24). When racemic CHIRAPHOS is mixed with an enantiomerically pure Ir(I) complex that has two ( —)-menthyl (Z)-a-(acetam-ido)cinnamate ligands, (S,5)-CHIRAPHOS forms the Ir complex selectively and leaves the R,R enantiomer uncomplexed in solution. Addition of 0.8 equiv of [Rh(norbomadiene)2]BF4 forms a catalyst system for the enantioselective hydrogenation of methyl (Z)-a-(acetamido)cinnamate to produce the S amino ester with 87% ee. Use of the enantiomerically pure CHIRAPHOS-Rh complex produces the hydrogenation product in 90% ee. These data indicate that, in the solution containing both (S,S)-CHIRAPHOS-Ir and (/ ,/ )-CHIRAPHOS-Rh complexes, hydrogenation is catalyzed by the Rh complex only. 

A fairly large number of mixed carbonyl phosphine and arsine complexes have been reported so far. They are generally prepared by displacement of CO from Ni(CO)4. Owing to the high stability of Ni(CO)4, when it is reacted with phosphines and arsines at room temperature and atmospheric pressure, only a partial displacement of CO usually occurs. Most of the mixed phosphine (or arsine) carbonyl compounds have the general formula [Ni(CO) (PR3)4 ] (n = 3, 2) and [Ni(CO)2(L—L)] (L—L is a diphosphine or diarsine). These complexes are colourless or yellow-orange solids or liquids. Many of them are thermally stable but decompose in air. The most relevant mixed carbonyl complexes with common phosphines are reported in Table 4. 

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