Phosphine and Phosphite Complexes

Phosphine and Phosphite Complexes.—The following general scheme is characteristic of reactions of these complexes  

In the reaction of tetrakistriethylphosphitenickel(o) with cyclohexyl isocyanide, in n-hexane or benzene solution, the kinetics are first-order with rates independent of isocyanide concentration. Rates are, however, reduced by the addition of excess triethyl phosphite. Here the forward reaction of the initial equilibrium must be rate-determining, and the second reaction fast. Triethyl phosphite exchange with Pd[P(OEt)a]4 or Pt[P(OEt)a]4 also takes place by rate-determining loss of one ligand molecule. Activation energies are in the order Ni Pd Pt, as are the stabilities to thermal decomposition of M(PF3)4. A delicate balance of (7- and TT-bonding effects is needed to rationalise this trend.  

In many reactions, particularly of phosphine complexes, the above reaction scheme still applies, but with a rapidly established dissociative equilibrium followed by rate-determining reaction of ML3 with Y. This is the case in oxidative elimination reactions, which are discussed in the oxidative addition section. Sometimes the mechanism and products depend on conditions, as in reaction of Pt(PPha)4 with hydroxyacetylenes, where the nature of the solvent, the presence of excess of phosphine, and particularly the stereochemistry of the alkyne, all affect the course of the reaction.  

The kinetic behaviour of phosphite, phosphine, and carbonyl complexes has been compared.  

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A number of ruthenium(II) complexes have been prepared. Cole-Hamilton and Stephenson isolated cts-[Ru(Me2dtc)2L2] (L = PPhj, PMe2, Ph, PPhMe2, or P(OPh)3) from Ru(II) and Ru(III) tertiary phosphine and phosphite complexes with NaMe2dtc, and found that they undergo rearrangements (288). 

There are many phosphine and phosphite complexes of iron(O), sometimes acting as P,C-donors in orthometallated complexes. In general this area is deemed to be organometallic chemistry, so we shall cite just one recent reference to act as a possible point of entry to this area, relating to [Fe(CO)2 P(OPlfi3 P(OPh)2(OC6Fl4) which contains both a P- and a P,C-donor triphenylphosphite ligand. ... 

Table 7 Pt—P Distances in Platinum(II) Phosphine and Phosphite Complexes...

Preparation of phosphine and phosphite complexes of palladium ) have been reported to result from reduction of palla-dium(II) complexes in the presence of the desired ligand.1" The products are generally formulated as PdL4 (where n = 0, 1), depending upon the nature and amount of the ligand used. A related complex, [Pd P(C6H5)3 2]re, has also been reported.6... 

Ligand size determines coordination numbers as well as reactivity. Thus phosphine complexes of Pd°, frequently used as precursors in palladium catalyzed reactions, may be 4-, 3-, or 2-coordinate, as in Pd(PMe3)4, Pd(PPr )3, and Pd(PPhBu 2)2, respectively. For nickel phosphine and phosphite complexes, the dissociation constant Kd for the equilibrium... 

Indirect observation of activation of arene C-H bonds in phosphine and phosphite complexes of Ru and Os was reported. ... 

Rhenium dinitrogen phosphine and phosphite complexes give products through intramolecular C-H activation upon ultraviolet (UV) irradiation in hydrocarbon solvents. For example, the agostic complex 88 identified by IR spectroscopy decays to stereoisomeric cyclometallated products [Eq. (6.68)]. Analogous transformations were observed for phenoxy and phenyl derivatives. 

Photolysis of Kr matrices containing HI and NiCCO) at 4 K leads to a new product vdilch on the basis of its ESR spectrum is thought to be the radical HNl(CO),. This has a trigonal geometry and a A, ground state of C,y symmetry.The first exaunples of d ° metal phosphine and phosphite complexes of Ml, Pd, auid Pt which possess long-lived emissive excited states in fluid solution at room temperature have been described these con lexes are photochemically reactive towards orgwlc substrates. 

The phosphine and phosphite complexes of rhodium, cobalt, and platinum are commonly used as catalysts for hydroformylation of olefins (Eq. 7). Other... 

Platinum(II)-phosphorus distances in phosphine and phosphite complexes are usually between 2.2 and 2.4 A. The distances are affected by the ligand trans to phosphorus in the square plane. For a complete listing of platinum-phosphorus distances in such structures the reader is directed to Molecular Structures and Dimensions for structures from 1935-1976, and to the BIDICS series for structures published up through 1981. A list of representative structures and Pt—P bond distances is shown in Table 7. The Pt—Cl distance of 2.344(2) A in cis-PtCl2(PEt3) P(OPh)3 for the chloride trans to P(OPh)3 is shorter than that (2.355(2) A) for the chloride trans to PEts, implying a weaker trans influence of P(OPh)3 than of PEt3. ... 

Halogeno-phosphine and -phosphite complexes, cis- and trans-isomers of [PdCl2(PMe2-o-tolyl)2] have been prepared... 

Metal basicity is also exhibited by phosphine and phosphite complexes of nickel(0), which can be protonated by acids of various strengths ... 

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