Transition metal phosphides, addition

The transition metal-free addition of silylphosphines to styrenes, pyridines, and acrylates was promoted by a fluoride source (Scheme 4.17) [59]. The addition reaction occurred under extremely mild conditions and afforded moderate to excellent yields of the anti-Markovnikov addition prodnct. The reaction was proposed to proceed through initial formation of a phosphide anion that reacted with the alkenes through a phospha-Michael-type addition. The proton source for the generation of the final adduct was proposed to be adventitious moisture in the commercially available TBAF solution. While activated alkenes were quite amenable to this approach, unactivated alkenes were unresponsive. 2-Vmylpyridine was particularly reactive and was cleanly converted into the alkylphosphine (95%). While most of the substrates were terminal Michael acceptors, a number of internal alkenes as well as a tetrasubstituted alkene were converted into the alkylphosphines in moderate yields (Schane 4.18 and Example 4.17). The chemistry could be extended to terminal and internal alkynes, although a mixture of E- and Z-isomers were obtained with the EIZ> 1. Following this work, the authors were able take advantage of the need for another electrophile to complete the reaction and added an aldehyde to trap the intermediate carbanion [60]. This approach worked well and enabled the construction of gamma-hydroxyphosphonates in excellent yield (up to 88%). 

The transition metal-free addition of sodium phosphides to protected alkynols proceeds under mild conditions to selectively form the 1,1-addition products (Scheme 4.286) [73]. The alcohol was deprotonated prior to the addition of the anionic phosphorus reagent to ensure the selective addition to the alkyne. The lithium alkoxide was hydrolyzed after the P—C bond-forming reaction was obtained. The conditions were extremely mild, and moderate yields of the addition product were obtained. 

The extension of this approach to artificial leaves based on titanates, niobates, tantalates, metal nitrides and phosphides, metal sulfides, and other transition metal oxides appears possible and useful in order to enhance the photocatalytic efficiency. In addition, the construction of multicomponent systems such as Ti02-CdS or MoS2-CdSe for overall water splitting could also lead to further improvements. This... 

Hydrophosphination of carbodiimides to yield phosphaguanidines was catalyzed by several related metal complexes. For example, after carbodiimide coordination by the calcium phosphide complex 12 (see Scheme 18 above), P-C bond formation involving a four-centered transition state and rearrangement was proposed to yield the N,N-bound intermediate 13. Addition of the P-H bond across the Ca-N bond, followed by dissociation of the product, then regenerates the phosphide intermediate (Scheme 23) [37]. Related chemistry was reported recently using the calcium phosphide complex Ca(PPh2)2(THF)4 [38]. 

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