Phosphorus electron donors

Towards a simple Lewis base, for example the proton, phosphine is a poorer electron donor than ammonia, the larger phosphorus atom being less able to form a stable covalent bond with the acceptor atom or molecule. Phosphine is, therefore, a much weaker base than ammonia and there is no series of phosphonium salts corresponding to the ammonium salts but phosphonium halides. PH4X (X = Cl, Br, I) can be prepared by the direct combination of phosphine with the appropriate hydrogen halide. These compounds are much more easily dissociated than ammonium halides, the most stable being the iodide, but even this dissociates at 333 K PH4I = PH3 -t- HI... 

Phosphorus trifluoride is a colourless gas the molecule has a shape similar to that of phosphine. Although it would not be expected to be an electron donor at all (since the electronegative... 

Ti -Cyclopentadienyl(triphenylphosphine)cobalt reacts with phosphites and forms complexes of 1-alkoxyphosphole oxides 251 (R = Me, Et, Ph) through a step involving (ri -cyclopentadienyl)(phosphite)cobalt (80JA4363). (ri -Cp)Co(PF3)2 reacts with hexafluorobut-2-yne and 252 is formed, which hydrolyzes into 253 (X = OH) [73JCS(CC)583 75JCS(D)197]. The five-member ring has the envelope conformation, in which the carbon atoms are coplanar, and the phosphorus atom deviates from this plane in the direction opposite to the cobalt atom. The heterocycle is a four-electron donor relative to the metal center. 

Table 2 Geometric parameters for halogen bonded complexes with phosphorus and sulfur electron donors... 

Phosphonium ylides, which can be written in the two familiar canonical forms, are available with a wide variety of substituents both at the phosphorus and at the carbon atoms (Scheme 30). In gold complexes, without any exceptions, they function as two-electron donors, as proposed by the dipolar form to give discrete Au-C cr-bonds (771, monohapto). No side-on, 7r-coordination (t 2), as might be expected out of the ylene form, has been observed to date. 

As an alternative to QDs, silicon can be doped with single atom impurities, in particular phosphorus, which acts as an electron donor. Donors can be implanted individually with a precision of about 10 nm. Either the 31P nuclear spin or the unpaired electron can be used as qubits [63, 64]. An advantage of silicon is its widespread use in current electronics, meaning that QC might profit from methods and technologies already developed for their classical cousins . Also, spins in silicon can attain extremely high coherence times experiments on 28 Si-enriched silicon show spin coherence times T2 exceeding 10 s [65]. The read-out and coherent manipulation of individual spin qubits in silicon have been recently achieved [66]. 

Although the subject of stability of complexes will be discussed in greater detail in Chapter 19 it is appropriate to note here some of the general characteristics of the metal-ligand bond. One of the most relevant principles in this consideration is the hard-soft interaction principle. Metal-ligand bonds are acid-base interactions in the Lewis sense, so the principles discussed in Sections 9.6 and 9.8 apply to these interactions. Soft electron donors in which the donor atom is sulfur or phosphorus form more stable complexes with soft metal ions such as Pt2+ or Ag+, or with metal atoms. Hard electron donors such as H20, NH3( or F generally form stable complexes with hard metal ions like Cr3+ or Co3+. 

As can be seen from Figure 3b and 3d continuous flow systems bypass wastewater and recycle sludge to develop flexibility. Recycling is directed mostly to the first reactor. Bypass flow typically goes to anoxic or anaerobic tanks to supply electron donors for the removal of phosphorus and/or for denitrification. The equivalent action in an SBR is the application of aeration and mixing during react (except after static fill). 

For some reviews, see (a) Majoral J-P (2007) Influence of cationic phosphorus dendrimers on the surfactant-induced synthesis of mesostructured nanoporous silica. New J Chem 31 1259-1263 (b) Puntoriero F, Nastasi F, Cavazzini M et al (2007) Coupling synthetic antenna and electron donor species a tetranuclear mixed-metal Os(II)-Ru(II) dendrimer containing six phenothiazine donor subunits at the periphery. Coord Chem Rev... 

That these P4-related tetrahedral clusters retain donor capacity through the phosphorus atoms was illustrated by the isolation of adduct 5 (the parent P[0o(00)3]3 cluster is unstable (38), in which the PO03 cluster behaves as a two-electron donor towards the unsaturated 16-electron Fe(00)4 moiety. The rather high 00 vibration frequencies in the infra-red spectrum indicate again that the cluster also has some TT-accepting capacity. Further manifestation of the donor character of this phosphorus atom can be seen in its tendency to readily d.isplace 00 from a 00(00)3 moiety... 

Tolman, C.A. (1970) Electron donor-acceptor properties of phosphorus ligands. Substituent additivity. J. Am. Chem. Soc., 92, 2953-2956. 

A typical structure of these so called triple-decker sandwich complexes is that of the complex [(p3)Ni -(j)3-P3) Ni(p3)](BPh4)2-2.5Me2CO (73). In each complex the trihapto P3 (or trihapto As3) groups form a bridge between the two Ni(p3) residues.292 Each nickel atom is thus six-coordinated by three phosphorus atoms from the ligand p3 and by three phosphorus atoms from the cyclo-P3 (or arsenic atoms from the cyclo-As ), which acts as a three-electron-donor ligand. 

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