Phosphines monodentate tertiary

Pt(en)(N03)2] and [Pt(OTf)2L2] (L = mono- or 1/2 bidentate tertiary phosphine) or dinuclear complexes of the type [Pt2(OTf)2(/i-other structural motifs employing platinum(II) have also been reported.2 0 The addition of bridging, multidentate N-donor ligands of various shapes and sizes to the labile complexes in a suitable solvent system has afforded several classes of discrete, plat-inum(II)-containing polygons, polyhedra, and catenanes. 

The first examples of five-coordinate platinum(II) complexes of the type [Pt(PR3)L]2+ (L = tris(2-(diphenylphosphino)ethyl)phosphine R = Et, OMe, OEt) (104) containing only P-donor atoms have been prepared by the reaction of [PtClL]+ with an appropriate monodentate tertiary phosphine or phosphite ligand.284 Triaryl phosphines and phosphites do not react with the precursor complex, even at elevated temperatures, most probably due to the considerable steric interactions that would occur upon the approach of the P-donor ligand to the platinum(II) center. 

During the late 1960s, Homer et al. [13] and Knowles and Sabacky [14] independently found that a chiral monodentate tertiary phosphine, in the presence of a rhodium complex, could provide enantioselective induction for a hydrogenation, although the amount of induction was small [15-20]. The chiral phosphine ligand replaced the triphenylphosphine in a Wilkinson-type catalyst [10, 21, 22]. At about this time, it was also found that [Rh(COD)2]+ or [Rh(NBD)2]+ could be used as catalyst precursors, without the need to perform ligand exchange reactions [23]. 

Complexes with monodentate tertiary phosphines, arsines and stibines 108... 

Complexation of SnHaLt (Hal = Cl, Br) with monodentate tertiary phosphines (PI13P, Ph2MeP, PhMe2P and BU3P) has been studied by 119Sn and 31P NMR spectroscopies in CH2CI2 solutions at various donor/acceptor (D/A) ratios and depend on the temperature (-90 °C and +3 °C). Selected NMR parameters for the complexes are given in Table 78. 

TABLE 78. 31P and 119Sn NMR parameters for complexes of SnHaLj with monodentate tertiary phosphines in CH2C1226... 

There is an extensive chemistry of tertiary phosphine rhodium(III) complexes. However, there are comparatively few complexes of monodentate tertiary arsines, although the complexes of ditertiary arsines are more numerous. There are virtually no tertiary stibine complexes. The two main preparative routes to the complexes described in this section are (i) direct reaction pf the ligands with rhodium trichloride, which usually yields trichloro complexes and (ii) oxidative addition to rhodium(I) tertiary phosphine complexes, which gives rise to more diverse products of the type [RhXYZ(PRj) ], Metathetical reactions on the complexes prepared by either method (i) or (ii) have been used to prepare most of the remaining compounds. 

Why this product is formed rather than the metal-metal bonded dimer Re2(NCS)6(PR3)2, which would be analogous to the Re2Cl6 (PR3)2 dimers that are formed initially upon reacting Re2Cla2 with monodentate tertiary phosphines(23.27). remains a puzzle. Dimers of type I may of course be the thermodynamically favored products (whereas Re2X6(PR3)2 dimers may not) and it is certainly true that spectroscopic evidence(32) favors a weaker Re-Re bond in Re2(NCS)82- compared to Re2Cl873, perhaps a hint that it is more susceptible to fission. Unfortunately, the mechanistic features of the reactions which lead to I are unknown. 

The second (and final) set of reactions which will concern us in this section are those in which acetonitrile solutions of the salts (Bui,N)2Re2X8 (X = Cl or Br) are converted to the centro-symmetric halogen-bridged dimers Re2Xe(LL)2(il) by l,2-bis(diphen-ylphosphino)ethane and l-diphenylphosphino-2-diphenylarsinoethane (33,3, 35). This behavior contrasts with the substitution using monodentate tertiary phosphines and arsines which gives rise to Re2X6(PR3)2 ... 

Knowles [1] and Homer [2] independently discovered homogeneous asymmetric catalysts based on rhodium complexes bearing a chiral monodentate tertiary phosphine. Continued efforts in this field have produced hundreds of asymmetric catalysts with a plethora of chiral ligands [7], dominated by chelating bisphosphines, that are highly active and enantioselective. These catalysts are beginning to rival biocatalysis in organic synthesis. The evolution of these catalysts has been chronicled in several reviews [8 13]. 

Unless stated otherwise, X = anion (usually halide) L = monodentate tertiary phosphine, arsine, or phosphite S = solvent. 

Pentacarbonyliron and Fe2(CO)9 react with monodentate tertiary phosphines, arsines, and stibines to give substitution products of the general formula Fe(CO)j (ER3) . Usually substitution does not proceed beyond n = 2 ... 

Silver(I) derivatives containing monodentate tertiary phosphines PR3 (R = Ph, Bn, o-Tol, m-Tol, p-Tol) and HB(tz)3 have been also... 

In the same way Ta(CHCMe3)(OCMe3)2 reacts with cis-2-pentene to give the initial and productive metathesis olefins but deactivates without formation of propylene and ethylene. In this case the chain termination steps must be a bimolecular decomposition of the alkylidene intermediates. Adding monodentate tertiary phosphine increases the lifetime of the complex, probably by a stabilizing effect of the alkylidene intermediates. 

Several technetium(IIl) complexes containing both tetradentate Schiff-base and monodentate tertiary phosphine ligands have been synthesized. [Tcj(acac)2enj (PPh3)2 was obtained by reaction of [TcOCU] with H2(acac)2cn and PPh 3 in methanol ... 

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