Phosphites bonding properties

We wish to report several metal complexes formed from a phosphorous acid diester of the type OP (H) (OR) 2 which underwent isomerization to form a metal-phosphorus bond as in (a). In the course of our investigations on the complexing properties of polycylic phosphites (9 17) j it was found that 2,8,9-trioxa-l-phosphaadamantane (L) undergoes a rapid, acid hydrolysis in acetone to form two colorless, crystalline hydrolysates, A and B. Only isomer A or L complexed with divalent hydrated metal ions, and it is concluded from infrared evidence that A has isomerized as shown in the following reaction sequence. Supporting infrared and PNMR evidence is presented for the tentatively postulated structures of A and B. 

This chapter will be limited to the preparation and properties of compounds (2) with one or two P—C bonds, since only these compounds contain functional groups of phosphorus in the sense of the Patai series. Thus, important classes of tervalent phosphorus acid derivatives with three electronegative groups, e.g. phosphites (3), tris(dialkylamino)phos-phines (4) and phosphoramidites (5), will only be included for illustration of a reaction or property which is common to tervalent phosphorus acid derivatives but has not been sufficiently studied for compounds with a P—C bond. The chapter will cover the highly reactive, dicoordinated derivatives 6, but not diphosphines 1 (X = PR2) or diphosphenes 6 (X = PR). 

Replacement of one PEts ligand by a phosphite leads to new series of phosphine/phosphite or bis(phosphite) complexes the differences in ability to promote HDS were accounted for in terms of donor-acceptor properties of the ligands involved in each case. Thiophene substituted with groups other than alkyls (e.g., -Cl, -NO2, -OMe, -OAc) also form thiaplatinacycles, which are notable in that they promote catalytic desulfurization. These substituted thiophenes also produced the first thiapalladacycles by reaction with the corresponding Pd-phosphine complexes, as well as Ni analogs.3,6-Dimethylthieno[3,2- ]thiophene also forms a thiaplatinacycle by activation of a C(vinyl)-S bond upon reaction with [Pt(PEt3)4] 2,2 -bithiophene and l-methyl-2-(2-thienyl)pyrrole react similarly but also promote G-H activation. 

The idea of metal-metal bond establishment in the excited state of this complex has also stimulated the interest on the photophysical and photochemical investigations of related d -d complexes. In 1970, Dori and co-workers first reported the luminescence properties of phosphine complexes of d metal centers such as copper(I), silver(I), gold(I), nickel(0), palladium(0), and platinum(0) [12]. Later in 1985, Caspar reported the luminescence properties of polynuclear nickel(O), palladium(O), and platinum(O) complexes of phosphine, phosphite, and arsine [13]. Similar to the related d -d systems, the emissive states of [Pd2(dppm)3] and [Pd Cdpam),] have been suggested to be metal-centered (d-p) in nature modified by metal-metal interaction. 

Espinet and coworkers examined gold complexes of ADC ligands containing a hydrogen-bonded backbone - denoted hydrogen-bond supported heterocyclic carbenes (HBHCs) - in cyclizations of 1,6- and 1,7-enynes and observed unusual selectivities [27a]. Catalysts 24a and 24b were found to fevor the endo cycliza-tion product in reactions of enyne 23, whereas previously known phosphite-(25) and NHC-based (26) catalysts favored the exo product (Scheme 16.9). Notably, the differing steric bulk of 24a and 24b did not appear to impact the exo endo ratio, suggesting that the observed selectivity depends primarily on the donor properties of the HBHCs. 

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