Chelate complexes bisphosphines

The most important contributions in this area, however, directly related to bond activation chemistry, and, undoubtedly triggered by theoretical considerations along the lines of Figure 1, were reported by Whitesides and coworkers in 1986 and 1988 [11]. It was shown that the bent, bisphosphine-coordinated platinum chelate complex [(dcpe)Pt(O)] (9) (dcpe = bis(dicyclohexylphosphino)ethane), which could be generated thermally as a "hot" reactive intermediate by reductive elimination of neopentane from its ris-neopentylhydride Pt(II) precursor at around 60-70°C in solution, was able to activate C-H bonds, even of unactivated alkanes. 

Nowadays we look with other eyes at organometallic compounds the family of which has expanded enormously. Some members of this family are soluble in water due to their ionic nature the legions of anionic carbonylmetallates (e.g. [Ni(CN)(CO)3] ) and cationic bisphosphine Rh-chelate complexes (e.g. [Rh(BDPP)(COD)] ) just come to mind. Others obtain their solubility in water from the well soluble ligands they contain these can be ionic (sulfonate, carboxylate, phosphonate, ammonium, phosphonium etc. derivatives) or neutral, such as the ligands with polyoxyethylene chains or with a modified urotropin structure. 

The tris(triphenylphosphine) rhodium carbonyl hydride complex also was used via ligand exchange to obtain known chelate complexes of bisphosphines... 

For cis-chelate complexes of rhodium and bisphosphines as catalysts, indeed relatively low ratios of n/i aldehyde products were reported (12, 13). Using a 1 1 mixture of H CO at atmospheric pressure, Sanger reported n/i ratios ranging from 3 to 4 for propylene hydroformylation (12). However, his catalyst systems were produced by adding less than 2 mol of bisphosphine per mole tris(triphenyl-phosphine)rhodium carbonyl hydride. When an excess of the chelating bisphosphines was used by Pittman and Hirao (13), low n/i ratios close to 1 were produced from 1-pentene using a mixture of H2/CO at 100-800 psi between 60° and 120°C. 

Chelate Complexes Derived from Tris(triphenylphosphine)rhodium(l) Carbonyl Hydride and Bisphosphines... 

Table II. Parameters of Chelate Complexes of Trimethylene Bisphosphine...

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],... 

Stereostructures of the bisphosphine (64) and the cis chelate complex (65) were evaluated by quantum chemical calculations. 

The hydroboration of enynes yields either of 1,4-addition and 1,2-addition products, the ratio of which dramatically changes with the phosphine ligand as well as the molar ratio of the ligand to the palladium (Scheme 1-8) [46-51]. ( )-l,3-Dienyl-boronate (24) is selectively obtained in the presence of a chelating bisphosphine such as dppf and dppe. On the other hand, a combination of Pdjldba), with Ph2PC6p5 (1-2 equiv. per palladium) yields allenylboronate (23) as the major product. Thus, a double coordination of two C-C unsaturated bonds of enyne to a coordinate unsaturated catalyst affords 1,4-addition product On the other hand, a monocoordination of an acetylenic triple bond to a rhodium(I)/bisphosphine complex leads to 24. Thus, asymmetric hydroboration of l-buten-3-yne giving (R)-allenyl-boronate with 61% ee is carried out by using a chiral monophosphine (S)-(-)-MeO-MOP (MeO-MOP=2-diphenylphosphino-2 -methoxy-l,l -binaphthyl) [52]. 

The number of phosphine ligands on the active catalyst system is also subject to speculation. In Scheme 9 Hata postulated an active complex consists of only one chelating phosphine. However, he (66) and others (70, 71, 83) also observed that 2 moles of the bisphosphine 32 per mole of Co are needed for best selectivity. Sarafidis (55) suggested that a more desired structure might consist of two bisphosphines, with one of the Co—P bonds having the ability to dissociate to provide coordination sites for incoming monomers (see structure 34). 

Even though the outlined approach allowed the successful rationalisation of many experimentally observed shift/structure and shift/reactivity correlations, Leitner et al. have pointed out that such relations cannot be expected to be universally valid and require that structural variations are modest and avoid large simultaneous changes in parameters that may have opposite effects on metal chemical shifts.61 To overcome these drawbacks and establish a more rational interpretation of chemical shift trends, they used a combination of experimental and computational efforts to assess the importance of different electronic and structural factors on the metal chemical shifts of a series of rhodium complexes with bidentate chelating bisphosphine ligands. The basis of their approach is first the validation of experimentally observed metal shifts by... 

The chiral phosphine 31 or 32-rhodium complex catalyzed the addition of arystannanes 30 to N-sulfonylimines 29 to give diarylmethylamines 33 with high enantioselectivity (75-96% ee) [21]. The choice of the chiral monoden-tate phosphine ligand is essential for their catalytic asymmetric arylation. With chelating bisphosphine ligands the arylation was very slow. The authors hypoth-... 

Nickel catalyst complexed with unfunctionalized chelating bisphosphine ligands, (R,R) norphos (75) 151 ] and 76 [ 19,52], also induced a high selectivity in the reaction shown in Scheme 8F.5 (Table 8F. 1, entries 38-39). The results reported with other phosphine ligands 33, 77-80 [30,53-56] are summarized in the Table 8F.1 (entries 40-44). 

P-31 NMR Studies of Equilibria and Ligand Exchange in Triphenylphosphine Rhodium Complex and Related Chelated Bisphosphine Rhodium Complex Hydroformylation Catalyst Systems... 

P-31 NMR studies also were carried out in a similar manner on rhodium complexes of two chelating bisphosphines—bis-l,3-diphenyl-phosphinopropane and bis-l,2-diphenylphosphinoethane. These complexes were generated in solution via ligand displacement from tris(tri-phenylphosphine)rhodium carbonyl hydride. For example, one of the possible displacement products of bis-l,3-diphenylphosphinopropane (F) is a cis-chelate (G) that can undergo dissociation to yield a chelating bisphosphine complex (H) ... 

An interesting synthesis of the cyclopentadienyl bisphosphine ruthenium nitrosyl complex 9 involves the thermal displacement of both phenyl groups from (i75-C5H5)Ru(NC))PIi2 (8) with a chelating diphosphine [Eq. (6)] (72). Infrared data indicate that the nitrosyl ligand is linear (3 e ... 

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