Polyphosphine ligands

The complex consists of a bis(diphosphinomethanide) ligand binding a lithium atom at each end in an t/2-PP coordination mode [Li-P = 2.542(6) and 2.559(6) A]. The lithium atoms achieve four-coordination through the coordination of two molecules of THF each. Hydrolysis of this complex is an excellent route to the otherwise inaccessible tetraphosphine (Ph2P)2CHCH2 2, a potentially useful polyphosphine ligand analogous to two linked bis(diphenylphosphino)-methane (dppm) moieties. 

The solutions of alkali pentaphospholides MP5 are gold-orange to red in color and are extremely sensitive to oxidation. The pentaphospholide ion P5 reacts with alkyl halides RBr and RI. The alkyl pentaphospholes RP5 which are to be assumed as the primary products are non-aromatic and unstable, however, and rearrange to alkyl polyphosphines such as R3P7 and R3P9 <88AG288>. The trimethylsilyl pentaphosphole is known as a complex ligand (see Section 4.22.12.1.2). 

Five-coordination is now quite common in nickel(II) complexes and many polydentate ligands such as polyamines, salicylaldimines, polyarsines and polyphosphines have been designed with the purpose of favouring this stereochemistry.7,8 However, five-coordinate complexes with monodentate ligands ([Ni(CN)s]3 and [Ni(OAsMe)s]2+) are also known. 

The phosphorus macrocycles are made via template condensation of coordinated polyphosphine ligands and a dibromoalkane (equation 8).60 A more recently reported method involves a template-assisted single-stage ring closure (equation 9).61 The arsenic donor macrocycles are synthesized by reacting lithiated polyarsanes with a dichloroalkane (equation 10).62... 

The rhodium(III) complexes can be prepared either by oxidative addition to the corresponding rhodium(I) complexes or by direct reaction of the ligands with rhodium(ITI) salts. Normally the reducing properties of tertiary polyphosphines ensure that rhodium(I) complexes are formed hence the rhodium(III) complexes of these ligands have been prepared via oxidative addition reactions. However, the sterically hindered ligand (105) fails to reduce hydrated rhodium trichloride even when allowed to react with the latter in refluxing ethanol (equation 260).235... 

As for the tr-donor and jr-acceptor properties, a useful generalization is that as the average electronegativity of the three groups attached to P increases, the ligand becomes a poorer tr-donor but a better jr-acceptor. With polyphosphines the tr-donor/jr-acceptor properties of each phosphorus atom will be governed by the same rules that apply in a monophosphine, but additional steric considerations come into play based on how the two or more phosphorus atoms are connected. 

By using a combination of known reactions, synthetic chemistry, and electrochemistry, new catalysts for the electrochemical reduction of CO2 have been developed. Consideration of the electrochemical properties of a variety of transition metal complexes containing polyphosphine ligands led to a more detailed study of metal complexes of the type [M(PP2)(PR3)HbF )2 (where M is Ni, Pd, and Pt ... 

The clean introduction of clusters onto the termini of polyphosphine dendrimers is a real challenge because of the current interest of dendritic clusters in catalysis and the mixtures usually obtained in thermal reactions of [Ru3(CO)i2] with phosphines.37 The diphosphine CH3(CH2)2N(CH2PPh2)2 (abbreviated P-P) was used as a simple, model ligand. The reaction between P-P and [Ru3(CO)i2] (molar ratio 1/1.05) in the presence of 0.1 equiv. [Fe p 6-C6Me6)] in THF at 20°C led to the complete disappearance of [Ru3(CO)i2] in a few minutes and the appearance of a mixture of chelate [P-P. Ru3(CO)i0], monodentate [P-P. Ru3(CO)n], and bis-cluster [P-P. (Ru3(CO)n 2]. These reactions were reported by Bruce et al. with simple diphosphines.38 On the other hand, the reaction of P-P with [Ru3(CO)i2] in excess (1/4) and only 0.01 equiv. [FeICp(r 6-C6Me6)] in THF at 20°C led, in 20 minutes, to the formation of the air-stable, light-sensitive bis-cluster [P-P. Ru3(CO)n 2] as the only reaction product. Given the simplicity of this characterization of the reaction product by 31P NMR and the excellent selectivity of this model reaction when excess [Ru3(CO)i2] was used, the same reaction between Reetz s dendritic phosphines,39 derived from DSM s dendritic amines,40 and... 

More recent work on the hydrogenation of thiophenic molecules catalyzed by water-soluble metal complexes is pursuing the use of polyphosphine ligands (cf. Section 3.2.2). These studies follow the success obtained with the tridentate phosphine MeC (CH2PPh2)3 (TRIPHOS), which forms rhodium and iridium catalysts for the hydrogenation, hydrogenolysis, and desulfurization of various thiophenic... 

Polyphospha macrocycles can be made via template condensations of coordinated polyphosphine ligands and dibromoalkanes (Scheme 6). ... 

Pd nanoparticles were similarly prepared through decomposition of Pd2(dba)3 under H2 in the presence of HDA or polyphosphines as stabilizers. The influence of the ligands on the particles shape was established good ligands like polyphosphines lead to stable spherical nanoparticles of small size (near 2nm) while the HDA protective effect... 

Structure and Reactivity Patterns of Polyphosphine Ligands and Their Complexes of Rhodium and Cobalt(I)... 

This paper is concerned with all these five aspects of polyphosphines. In addition, the methods for synthesizing polyphosphine ligands are discussed briefly. 

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