Phosphines redox reactions

See Other METAL PHOSPHINATES, REDOX REACTIONS, REDUCANTS... 

BU3P. A rapid redox reaction takes place to yield the active Pd(0) species and tributylphosphine oxide. The Pd(0) thus generated is a phosphine-free cata-lyst[341]. Severe reaction conditions are necessary, or no reaction takes place, when Pd2(dba)3 is used in the elimination reaction of cyclic allylic compounds with an excess of -Bu3P[342]. 

The complex reacts with CO reversibly via a series of redox reactions. Rh(TMPP)2+ forms adducts with bulky isocyanides RNC (R = Bu , Pr ), retaining the +2 state but changing to a trans-geometry (Figure 2.34) with monodentate phosphines (and uncoordinated ethers) (R = Bu , Mefr = 2.04 B gj. = 2.45, g = 1.96). 

The ethanal was converted to its 2,4-DNP derivative, obtained in 87% yield.) It may also be noted that for this redox reaction, iridium retains the +3 state throughout. The more labile chloride trans to phosphine is replaced... 

The reasons for this are not clear (40). I5N-Labeling studies on the protonation reaction between HBr and Mo(N2)2(PPh3)(triphos)] show that the dinitrogen released in both fast and slow stages is formed without new N—N bonds being formed. These observations together with the prerequisite for a monotertiary phosphine and the stoichiometry of reaction (49) have been rationalized by an intramolecular redox reaction such as is represented by Scheme 13 (40). However, certain aspects of this Scheme have yet to find empirical support. 

Similarly, a recent study141 of the homogeneous oxidation of cyclohexene by various low-valent phosphine complexes of Group VIII transition metals yielded no definite proof for initiation by oxygen activation. Results were consistent with reactions involving chain initiation via the usual redox reactions of the metal complexes with traces of hydroperoxides. Long induction periods were observed with peroxide-free hydrocarbons. 

Proton NMR spectroscopy was employed to follow complex formation on titration of V,7V-bis[ 6-(hydroxymethyl)-pyridine-2-yl methyl]-p-tosylamide (= L) with Cu(I) and Zn(II) salts (giving (L)Cu1, (L)Zn11).1163 31P NMR spectra were used to follow oxidative-addition reactions of (L)AuX + X2 (X = Cl, Br L = phosphines, phosphates), showing a reluctance by very bulky L ligands to undergo such reactions.1164 Similar data were obtained for redox reactions of (R3P)2AuBr with diselenides (R = Me, Et).1165... 

In electrochemical redox reactions it is thought that the electron is transferred through the carbonyl ligand. Cyclic voltammetry experiments, in which the separation of the anodic and cathodic waves can be viewed as a measure of the ease of electron transfer, have been used to indirectly show that the carbonyl ligand can mediate electron transfer (265). For example, the electron transfer rate is inhibited by bulky ligands for R CCo3(CO)9 BLB (n = 1-3 and L = PR3) (266, 267). The interpretation is that steric bulk of the phosphines prevents the cluster carbonyls from approaching the platinum... 

On the other hand, fluorination of alkyl- and aryldialkylaminochloro-phosphines, RPC1(NR2), with antimony (or arsenic) trifluoride under similar conditions to reaction (2) affords only the pentavalent fluoro-phosphorane RPFg(NR2) 288, 290) via the same type of redox reaction discussed previously in Section III,A for alkyl- and arylhalophosphines. 

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