Phosphido bridge reactivity

A Cautionary Note on Phosphido-Bridge Reactivity. Throughout this discussion of cluster and acetylide reactivity, the phosphido... 

Scheme X. Phosphido-bridge reactivity insertion into the bridge.

Wiped-Film Evaporator/02 Reactivation of Catalyst. In this technology [38], spent or-ganophosphine-modified rhodium catalyst is first concentrated in a wiped-film evaporator where most of the organophosphine is removed. The rhodium concentrate is contacted with air to break down phosphido bridges in rhodium clusters. This air treated concentrate may then be used as a catalyst precursor. This procedure is suitable in circumstances where most of the aldehyde dimers, trimers and tetramers are sufficiently volatile to be removed in a wiped-film evaporator. 

Equation 2.12. Reactivation of a phosphido bridged deactivated catalyst... 

We went back and looked at that system, because we thought it had quite a bit of promise. It turns out that, with triphenyl phosphine, platinum(O) will attack the phosphorous phenyl bonds to produce red polymers which are phosphido-bridged platinum species. But we were more interested in the small alkyl phosphines, because we expect those to make the metal center even more reactive (being sterically unhindered and more basic). 

Scheme L Phosphido-bridged complexes reactivity at other sites.

In this chapter we wish to focus on the synthesis, structural chemistry, and reactivity of some iron-group phosphido-bridged carbonyl clusters containing sideways-bound acetylides. The role of the PR2 group here is as a stable, unreactive, but flexible bridging coligand which facilitates exploitation of the unusual reactivity patterns for these /a2-7 2- and /Lt3-rj2-bound hydrocarbyl groups. 

Varieties of dinuclear cobalt complexes are known with two phosphido bridges. Those so far reported with the di-terf-butylphosphido ligand have two pseudotetrahedral 18-electron Co atoms linked by a metal-metal bond formally of order 2. Tetracarbonylbis(ii-di-terf-butylphosphido)-dicobalt( -t-1) can be prepared from the reaction of Co(CO)4l (generated in situ) with Li(r-Bu2P) in THE We describe here a simplified, high yield synthesis of this dimer via the interaction of Co2(CO)g with r-Bu2PH in toluene. The complex should prove to be a useful starting material for further reactivity studies. 

Scheme 12 Reactivity of phosphido-bridged dinuclear c

Bun, Bus, Bu1) (99). The complex with R = Me crystallizes as the THF solvate [MeCu(PBu2)Li(THF)3] in which the phosphide ligand bridges the two-coordinate Cu and four-coordinate Li centers. These cuprates were found to be more thermally stable than other phosphido(alkyl)-cuprates but less reactive toward electrophiles than related cyanocu-prates. 

Reactivity of Asymmetrically Bridged Phosphido Ligand Complexes... 

It is also pertinent to mention the occurrence of bridging phosphido and arsenido selenide ligands (Scheme 4).32 The phosphido selenide complexes (1 Scheme 4) were found to be very reactive and readily gave the six-membered heterocyclic complexes (3). In contrast the arsenido selenide systems gave both the four-membered ring intermediates (1 M = Mn, Re) and the six-membered heterocycles (3). 

Relatively few phosphido complexes of the transition metals are known that have an alkyl or aryl group (R) in addition to hydrogen attached to phosphorus [i.e., R(H)P"]. The reactivity of the P—unit has been studied in only a few cases. The syntheses described here are for dinuclear Rh( +1) or Ni( +1) complexes that have two t-BuP(H)" bridges. In both complexes the metals have pseudotetrahedral geometries. Of added interest for the rhodium complex is the presence of a Rh=Rh double bond. ... 

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