P donor

The simplest example is that of tire shallow P donor in Si. Four of its five valence electrons participate in tire covalent bonding to its four Si nearest neighbours at tire substitutional site. The energy of tire fiftli electron which, at 0 K, is in an energy level just below tire minimum of tire CB, is approximated by rrt /2wCplus tire screened Coulomb attraction to tire ion, e /sr, where is tire dielectric constant or the frequency-dependent dielectric function. The Sclirodinger equation for tliis electron reduces to tliat of tlie hydrogen atom, but m replaces tlie electronic mass and screens the Coulomb attraction. 

Until comparatively recently only vanadium had a significant coordination chemistry and even so the majority of its compounds are easily oxidized and must be prepared with air rigorously excluded. The usual methods are to use VCI3 as the starting material, or to reduce solutions of vanadium(V) or (IV) electrolytically. However, the reduction of pentahalides of Nb and Ta by Na amalgam or Mg, has facilitated the expansion of Nb " and Ta " chemistry particularly with S-and P-donor ligands. 

Azaphospholes where heteroaromaticity is regarded as appreciable, however, act mainly as (P) ligands, and often the P-donor carries two coordinated organometallic moieties. 

Tris(thiazol-2-yl)phosphine (L) and tris(benzothiazole-2-yl)phosphine (L) with [( j" -cod)PtMe2] give the cw-[L2PtMe2] complexes where the ligand is coordinated via its P donor center (73JOM(59)411, 76JA6521, 82JOC1489). 

The donor-acceptor formation can be considered by transfer of electrons from the donor to the acceptor. In principle one can assume donor-acceptor interaction from A (donor) to B (acceptor) or alternatively, since B (A) has also occupied (unoccupied) orbitals, the opposite charge transfer, from B to A. Such a view refers to mutual electron transfer and has been commonly estabUshed for the analysis of charge transfer spectra of n-complexes [12]. A classical example for a donor-acceptor complex, 2, involving a cationic phosphorus species has been reported by Parry et al. [13]. It is considered that the triaminophosphines act as donor as well as an acceptor towards the phosphenium cation. While 2 refers to a P-donor, M-donors are in general more common, as for example amines, 3a, pyridines, 3b, or the very nucleophilic dimethylaminopyridine (DMAP) [ 14], 3c. It is even a strong donor towards phosphorus trichloride [15]. 

Fig. 2. P-donor ligiind derivatives of MoFeCo(/r i-SHCO)s( ) -CsHs)].

Again, this aspect of carbon monoxide insertion has not received much attention. Hart-Davis and Mawby (108), in a comparative study, examined the reaction of 7r-C9H7Mo(CO)jMe (VII) with various P donor ligands. They find that, in THF, (VII) undergoes CO insertion, via a solvent-assisted... 

Recently, an abstract has been published 83) of a kinetic study of reactions of RMn(CO)3L2 (L = P donor ligand) with CO. No data were disclosed, however. 

Kinetic studies have been made of the reaction of CpMo(CO)j R (R = Me, Et, CH2Ph, and CH2CH=CH2) (48, 80, 81) and 7r-X2C9H5Mo(CO)jMe (X = H or OMe) (108) with a variety of P donor ligands L. Solvents employed ranged from nonpolar hexane to polar THF and MeCN. Generally, the mechanism is very sensitive to the coordinating ability of the solvent and the nucleophilicity of L. 

Photochemical reactions of CpFe(CO)2R [R = Me (227), Et (219), CH2SiMej (201), Rp (149), Ph (185-188), and various substituted Ph (187, 188, 190), inter alia] with L [L = PPh3, P(OPh)3, and related P donor ligands] almost invariably yield CpFe(CO)LR. Oftentimes, especially when elevated temperatures are employed, CpFe(CO)L(COR) is also produced (185,186,188) and is believed to arise through a competing thermal reaction. The observation that, under comparable conditions, the reaction (219)... 

The Rh and Ir complexes 85-88 (Fig. 2.14) have been tested for the intramolecular hydroamination/cyclisation of 4-pentyn-l-amine to 2-methyl-1-pyrroline (n = 1). The reactions were carried out at 60°C (1-1.5 mol%) in THF or CDCI3 The analogous rhodium systems were more active. Furthermore, the activity of 87 is higher than 85 under the same conditions, which was attributed to the hemilabihty of the P donor in the former complex, or to differences in the trans-eSects of the phosphine and NHC ligands, which may increase the lability of the coordinated CO in the pre-catalyst [75,76]. 

A detailed comparative study of the allylic substitution in allylacetates by amines has been carried ont for the two related mixed donor ligand systems 113 and 114 shown in Fig. 2.19. The P-C system shows dramatically lower activity than N-P, which has been atlribnted to the decreased electrophiUcity of the coordinated aUyl gronp, originating from the strongly o-donating NHC and P donors, compared to N and P donors. 

Neutral Pentafluorophenylgold(l) Derivatives with P-Donor Ligands... 

---