Transition metal—phosphine

A potentially interesting development is the microwave-assisted transition-metal-free Sonogashira-type coupling reaction (Eq. 4.10). The reactions were performed in water without the use of copper(I) or a transition metal-phosphine complex. A variety of different aryl and hetero-aryl halides were reactive in water.25a The amount of palladium or copper present in the reaction system was determined to be less than 1 ppm by AAS-MS technique. However, in view of the recent reassessment of a similarly claimed transition-metal-free Suzuki-type coupling reaction, the possibility of a sub-ppm level of palladium contaminants found in commercially available sodium carbonate needs to be ruled out by a more sensitive analytical method.25 ... 

A variety of Group VIII transition metal phosphine complexes are shown to be active catalysts for hydrogenation of aliphatic nitro compounds. However, chiral phosphines have been found to be noneffective to induce asymmetric induction.110... 

Pregosin, P. S. Kunz, R. W. NMR Basic Principles and Progress. 3IP and 13C NMR of Transition Metal Phosphine Complexes , Springer-Verlag Berlin, 1979. 

Ferraris et al.108 demonstrated an asymmetric Mannich-type reaction using chiral late-transition metal phosphine complexes as the catalyst. As shown in Scheme 3-59, the enantioselective addition of enol silyl ether to a-imino esters proceeds at —80°C, providing the product with moderate yield but very high enantioselectivity (over 99%). 

In the examples above, one or both of the reaction centers are already attached to the metal center. In many cases, the reactants are free before reaction occurs. If a metal ion or complex is to promote reaction between A and B, it is obvious that at least one species must coordinate to the metal for an effect. It is far from obvious whether both A and B enter the coordination sphere of the metal in a particular instance. A number of metal-oxygen complexes can oxygenate a variety of substrates (SOj, CO, NO, NO2, phosphines) in mild conditions. Probably the substrate and O2 are present in the coordination sphere of the metal during these so-called autoxidations. In the reaction of oxygen with transition metal phosphine complexes, oxidation of metal, of phosphine or of both, may result. The initial rate of reaction of O2 with Co(Et3P)2Cl2 in tertiary butylbenzene. 

Hydrophosphination is the addition of a P-H unit onto a double bond which can be catalyzed by transition metal phosphine complexes. In fact this reaction has been known for long [22,43] addition of PH3 onto formaldehyde serves as a basis for production of P(CH20H)3, a flame resisiting agent for wood and textiles. The details of this reaction have been recently scmtinized [38, 40], besides that the first hydrophosphination of an... 

NMR of Transition Metal Phosphine Complexes, Vol. 16, Springer Verlag, Berlin, 1979. 

Several workers have pointed out that there is a large and growing body of X-ray structural data of transition metal phosphine complexes. Such data can provide real cone angles, which may then be compared to Tolman s cone angles derived from models. Of course this line only applies to crystalline solids. Since the main application of transition metal chemistry is homogeneous catalysis, crystal structure data, though useful, are of limited applicability. Inevitably, cone angles in complexes in solution will be more variable than in crystalline systems. 

On this restricted basis, transition metal phosphines have been modeled with accuracies similar to those of other metal-heteroatom systems11531. A number of phosphine complexes are of interest in the area of asymmetric syntheses. Due to the requirement that the geometry and the force field of the relevant intermediates have to be known for a thorough study (see Chapter 7, Section 7.4) most of the reports in this area are only of a qualitative nature. Some of the investigations are based on molecular graphics analyses, and the evaluation of the predicted selectivity has been based on van der Waals terms alone[53,233,2341. 

Fig. 34. The relative energies of some transition metal phosphine and carbonyl fragments that are isolobal with CH or CH3.

P.S.Pregosin, R.W.Kunz 3lPand l3C NMR Transition Metal Phosphine Complexes... 

The most recent view on the 7t-accepting abilities of phosphines in transition metal-phosphine complexes is by Marynick 247) who has used approximate and ab initio MO theory to demonstrate that n accepting into o orbitals is important for PF3. Calculations on the model complex [Cr(NH3)5(PF3)] compared to [Cr(NH3)s(PH3)] showed... 

Insertions into transition metal-phosphine bonds have been observed, as shown in reactions (s) °, (t) and (u). ... 

Trimethylsilyl cyanide reacts with diphenylcyclopropenone in the presence of Fe2(CO)9 or PPh3 as catalyst to give the aminofuran derivative 73 (40-60%) (Eq. (10)). Other phosphines and transition metal phosphine complexes are effective catalysts. A similar reaction was achieved using cycloheptenocyclopropenone. Desilylprotonation of compound 73 was achieved in hot MeOH containing a trace of p-TsOH, but the primary amine was trapped in situ as a cycloadduct without isolation (87JOC4408). 

Transition metal phosphine complexes provide another important class of hydrogenation catalysts. Wilkinson s complexes, RhClfPPhjlj and RuHClfPPhjlj, well known for their olefin hydrogenation activity, were shown by Fish [77, 97] to be also good precursors for the reduction of polyaromatic substrates under mild reaction conditions (85° C, ca. 20 atm H, ). following a general activity trend consistent with a combination of electronic and steric factors ... 

Space constraints do not allow description of all the imaginative efforts to prepare, characterize, immobilize, and recover water-soluble transitional metal-phosphine complexes as hydrogenation catalysts. Further examples can be found in [11] and in [7[. For the mechanism of asymmetric hydrogenation of alkenes and that of the hydrogenation of aldeyhydes, see Section 6.2.3. 

The beneficial effect of water was observed in several experiments on reduction of C02. Inoue et al. were the first to discover that in the presence of a base (NaOH, NaHCOj, NMe3, NEt3, etc.) transition metal phosphine... 

Joe Chatt has been a pioneer of modern organometallic chemistry involving transition metal phosphine derivatives and in particular hydride complexes. In this article, we will emphasise the link between the pioneering work of Joe Chatt and the present interest in (T-bond complexes and their reactivity. This article concentrates on the chemistry of ruthenium derivatives and is divided into a brief historical overview, giving a perspective of the evolution of the chemistry of ruthenium hydride complexes and a part describing recent achievements in this field, mainly from our research group. 

Indeed, Mann s studies initiated an explosion of interest in transition metal phosphine chemistry. Chatt was Mann s student, and it is interesting to reflect that Chatt employed transition metal salts as a means of derivatising tertiary phosphines. Little did they realise how this area would expand Chatt s influence on metal-phosphine chemistry was profound, and out of it sprung the employment of phosphine complexes as tools for investigations into metal hydrides, nitrogen fixation, the stabilisation of unusual oxidation states, synthesis of metal alkyls and aryls, and the immense practical area of homogeneous and heterogen-... 

A general inspection of the Tables of published phosphorus chemical-shift data on co-ordination complexes (in Section VII) indicates the difficulties in any quantitative understanding. In general it appears that the majority of transition metal— phosphine complexes (particularly those containing the metal in its zerovalent state) have resonances at lower field than the corresponding unco-ordinated phosphine. On the other hand the chemical shifts of all phosphorus trichloride complexes occur at higher field than the free ligand, while the behaviour of phosphite complexes is rather more variable. Phosphine... 

Preparation of Phosphines by Addition of P-H to Unsaturated Compounds. -This route has not received much attention over the past year. A stereoselective synthesis of tris(Z-styryl)phosphine is offered by the addition of phosphine to phenylacetylene in a superbasic system (HMPA-H20-K0H)." In a similar vein, the reaction of phosphine with styrene and a-methylstyrene in a superbasic medium (DMSO-KOH) provides a route to the primary phosphines, (2-phenylethyl)phosphine and (2-methyl-2-phenylethyl)phosphine, respectively. 7 Transition metal phosphine complexes have been shown to catalyse the a-hydroxylation, P-cyanoethylation, and P-alkoxycarbonylethylation of phosphine. 71 Addition of primary phosphines to acrylic esters has been used for the synthesis of the phosphines (80).7 A similar addition of diphenylphosphine to acrylic esters and amides has given a series of hydrophilic phosphines (81). 72 The bis(phosphorinanyl)ethane (82) is formed in the photochemical addition of l,2-bis(phosphino)ethane to 1,4-pentadiene. ... 

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