Diphosphines carbonyl compounds

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. 

The oxidation of a nickel(O) carbonyl compound with halogens was employed by Chatt and Hart to prepare nickel(II) complexes with the diphosphine ligand (XVII R = Et equation 165) 1311 2 1 complexes were subsequently prepared by the direct synthesis of the reactants in acetone.1287... 

The mechanism of the enantioselective 1,4-addition of Grignard reagents to a,j3-unsaturated carbonyl compounds promoted by copper complexes of chiral ferrocenyl diphosphines has been explored through kinetic, spectroscopic, and electrochemical analysis.86 On the basis of these studies, a structure of the active catalyst is proposed. The roles of the solvent, copper halide, and the Grignard reagent have been examined. 

Dissymmetric ferrocenyldiphosphines have been synthesized from (R)-(+)-N, N -dimethylaminoethylferrocene. The diphosphines have been used as ligands in asymmetric transfer hydrogenation of acetophenone in the presence of ruthenium catalysts.297 Asymmetric transfer hydrogenation of a,/S-unsaturated aldehydes with Hantzsch dihydropyridines and a catalytic amount of MacMillan imidazolidinone salt (12) leads to the saturated carbonyl compounds in high yields and excellent chemo-and enantio-selectivities.298 ... 

In the synthesis of specially substituted methylene diphosphines, made from secondary phosphines and carbonyl derivatives (7), a carbenium ion adjacent to trivalent phosphorus as the transition state has been discussed. The transfer of this reaction principle to primary phosphines and suitable carbonyl compound revealed a further pathway to derivatives of dicoordinated phosphorus (8). Aromatic phosphines react with carboxylic acid amide acetals under elimination of alcohol giving dialkylamino-alkylidene phosphines (Scheme 5). A modification of the synthesis... 

Since the diphosphine is appreciably more electron-rich than is BINAP, the major ruthenium complex is a more active hydrogenation catalyst than the parent. Increased electron-rich ligation may be the reason for the success of heterocyclic analogues of BINAP in which the binaphthalene is replaced by a bi(ben-zothiophene) or biindolyl the resulting Ru complexes are effective both in terms of enantioselectivity and reactivity [139]. Readers of the related Chapter 6.1 on the asymmetric hydrogenation of carbonyl compounds will encounter the Ru complexes of ligands in the DUPHOS family, where the ease of modification of the alkyl substituents of the phospholane enhances the power of the system, since it permits the easy optimization of ee for any substrate [140]. 

It is of note that many of the clusters which were prepared by the method above (Section II,D,2,c) involve the reaction of a carbonyl compound with a ligand which can bridge between two metal atoms and, hence, assist in cluster formation. The diphosphines have been particularly effective in this way, and remain bridging in the final product. 

The diphosphine (R,S)-BPPFA [(R,pS)-9] reacts analogously with acetic anhydride to give the corresponding acetate which can be derivatized. Replacement of the acetate by hydroxide leads to a useful ligand BPPFOH 1534, which has been used for the rhodium-catalyzed enantioselective reduction of a-oxo acids to a-hydroxy acids (Section D.2.3.1.). Recently, the chemistry of gold(I) complexes of such chiral phosphines has been developed they catalyze aldol-type cycloadditions of isocyanides to carbonyl compounds to give chiral dihydrooxazoles. which can be hydrolyzed to synthetically important chiral amino alcohols and amino acids 30,39,40. 

Fig. 2 Chiral diphosphine ligands used in the ACA of Grignard reagents to a,p-unsaturated carbonyl compounds...

Harutyunyan et al. investigated the formation of the chiral Cu(I)-diphosphine complexes, as part of a comprehensive mechanistic study on the Cu(I)-catalysed ACA of Grignard reagents to a,p-unsaturated carbonyl compounds [127]. Based on NMR, ESI-MS, IR, electrochemistry and X-ray ciystaUography measurements, they concluded that halide-bridged dinuclear copper complexes Cl (Scheme 30) are formed and persist in the solvents typically used for the ACA (Et20, tBuOMe and CH2CI2). 

The expansion of this chemistry came by the work ofYun, since the copper borylation of a,P-unsaturated carbonyl compounds could be achieved by the activation of B2pin2 with CuCl in the presence of base and MeOH to favor the tr-bond metathesis. Remarkably, the use of chiral diphosphines to modify the Cu(I) salt was the key to dehver the Bpin moiety with asymmetric induction. A more detailed mechanism for the borylation of a,P-unsaturated carbonyl compounds was described by Lin with the aid of DFT calculations. The tr-bond metathesis step has also been elucidated, experimentally and theoretically, in the copper-catalyzed borylation of aryl hahdes with B2PUI2 by Marder and Kleeberg. 

Interest has developed recently in cyclopentadienylcobalt carbonyl complexes. Oxidative addition of RI (R = Me or Et) to CpCo(CO)L (L = PPh3, PMe2Ph, or PMePh2) yields initially CpCo(CO)RL I, which then undergoes rapid CO insertion to CpCoL(COR) . The slow step has been studied kinetically 148). Compounds of the type CpCo(CO)(Rp)I afford ionic substitution products when treated with chelating diphosphines 106). 

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 hydrogenation of ketones with O or N functions in the a- or / -position is accomplished by several rhodium compounds [46 a, b, e, g, i, j, m, 56], Many of these examples have been applied in the synthesis of biologically active chiral products [59]. One of the first examples was the asymmetric synthesis of pantothenic acid, a member of the B complex vitamins and an important constituent of coenzyme A. Ojima et al. first described this synthesis in 1978, the most significant step being the enantioselective reduction of a cyclic a-keto ester, dihydro-4,4-dimethyl-2,3-furandione, to D-(-)-pantoyl lactone. A rhodium complex derived from [RhCl(COD)]2 and the chiral pyrrolidino diphosphine, (2S,4S)-N-tert-butoxy-carbonyl-4-diphenylphosphino-2-diphenylphosphinomethyl-pyrrolidine ((S, S) -... 

The field of phosphorus- or arsenic-bridged compounds is very extensive, especially because of the work of R. G. Hayter and J. Chatt (96). We were able to isolate many /u-phosphido and /x-arsenido metal carbonyls by reacting diphosphines R2PPR2 or the corresponding diarsines (R = alkyl,... 

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