Phosphine addition

Lithiation at C2 can also be the starting point for 2-arylatioii or vinylation. The lithiated indoles can be converted to stannanes or zinc reagents which can undergo Pd-catalysed coupling with aryl, vinyl, benzyl and allyl halides or sulfonates. The mechanism of the coupling reaction involves formation of a disubstituted palladium intermediate by a combination of ligand exchange and oxidative addition. Phosphine catalysts and salts are often important reaction components. 

In compounds (333) and (336) the amines substitute one of the dithiophosphate ligands to form a NiN4S2 core with the second dithiophosphate ligand serving as a counterion. Coordination number 5 is rare, but is found for complex (345) where one of thiophosphates switched to a monodentate coordination,879 and in compound (346) where only one additional phosphine adduct coordinates to Ni.880... 

We conclude that only one phosphine attacks a ji-S group of 20. Indeed, the phosphine sulfide product from dmpm is Me2P(S)CH2PMe2, not a bis(sulfide).The other phosphine implicated by Eqs. (32) and (33), whether from a second PR3 or from a di-phosphine, adds as a Lewis base to rhenium. The basis for this is that a pyridine easily replaced one of the phosphines in the mechanism. This proposed mechanism should steer the reaction directly towards formation of 21, but owing to the dilemma posed in point (c), an intermediate likely intervenes. It can partition to the slowly-reacting 21 or to 23, the latter step requiring additional phosphine Scheme 13 shows the postulated mechanism. The dual role for phosphine and the use of Py in its place and the proposal for partitioning are shown in Scheme 14. 

Thus, while the behaviour of the mono-rhodium tetraphosphine complexes in homogeneous hydrogenation may be expected to correspond to that previously observed for Josiphos or Mandyphos if the additional phosphine act purely in a spectator mode, new behaviour may be observed if either of the two new cross-... 

Epimerization of vinylcyclopropanes by Grubbs I-type ruthenium catalysts (28) has been explored.33 The reaction can also be effected by the Grubbs-Hoveyda catalyst (29) provided that an additional phosphine is added. Mechanistic studies (experimental and theoretical) suggest that the epimerization goes through a ruthenacyclopentene intermediate (30). 

In compounds of the type R3P=CH-PR2 (8) an additional phosphine donor center is directly attached to the basic ylid carbon atom (16, 17). Novel derivatives of these ligands are, e.g., nickel complexes 9 containing the NiCPCP five-membered ring (18). 

C iCiimlfOTf] PPh3 1-Hexene 30-32(1.7-2.0) RhCl(PPh3)3 as catalyst precursor no additional phosphine [43]... 

C6)3C14P]C1 Pd2(dba)3 Et3N, K2P04 and others 50-70 °C. Activated chlorides can be coupled at 70 °C if additional phosphine ligand is present products extracted with hexane catalyst stable for at least 5 runs. [10-12]... 

Anderson and coworkers investigated the effect of added phosphine to solutions of Au(PR3)C126, which results in additional phosphine ligands attaching to a central gold atom as shown in equation 5. 

On the basis of the isolation of the intermediate compound 4 a reaction pathway was proposed (Scheme 1). Initially there is coordination of one phosphine with the formation of adduct III. This phosphine rearranges from axial to equatorial coordination with partial displacement of one acetate group. Proton transfer in this species IV yields the monometalated compound V, which further reacts with one additional phosphine to form the bimetalated compound. 

Interestingly these complexes showed high activity without addition of alkyl aluminum compounds in the ionic liquid while they are almost inactive in toluene. These results are interpretable in terms of catalyst stabilization by the imidazolium-based ionic liquid. Reductive elimination of imidazolium is also possible as in toluene as in the ionic liquid but in the ionic liquid, a rapid reoxidation via addition of the solvent imidazolium cation seems possible and may prevent the formation of Ni deposits associated with catalyst deactivation. The carbene complex with R = n-Bu showed the highest activity with a dimer yield of 70.2% (TOF = 7020 h ). The preferred product of the nickel-catalyzed reaction is methylpentene. Additional phosphine ligand had no significant influence on the distribution of the products in this case. 

Ferrocenylgold compounds have been prepared by the organoUthium method and auration of one or both of the cyclopentadienyl rings could be achieved. Similar to tetraphenylcyclopentadienylgold(l) phosphine complexes, these compounds can incorporate additional (phosphine)gold(l) units upon interaction with (triphenylphosphine)gold(l) tetrafluoroborate to give electron-deficient species as described below. 

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