Intramolecular C-C bond formation from beta-keto phosphine and allenylidene ligands in related ruthenium(II) cyclopentadienyl and indenyl complexes. X-ray crystal structure of (S-Ru,R-C/R-Ru,S-C)-[Ru(eta(5)-C9H7)(PPh3){eta(2)(P,O)-Ph2PCH(Me)C(Bu-t)=O}][PF6] and (S-Ru,R-C/R-Ru,S-C)-[Ru{eta(2)(C,P)-C(=C=CPh2)CH[C(=O)Bu-t]PPh2}(eta(5)-C9H7)(PPh3)]

The reaction of beta-keto phosphines Ph2PCH(R')C(=O)R (a, R = Bu-t, R' = H; b, R = Ph, R' = H; c, R = Bu-t, R' = Me) with [RuCl(eta(5)-CnHm)(PPh3)(2)] complexes (1, CnHm = cyclopentadienyl; 1', CnHm = indenyl) affords neutral [RuCl(eta(5)-CnHm)(PPh3){eta(1)(P)-keto phosphine}] (2a,b and 2'a), Cationic derivatives, [Ru(eta(5)-CnHm)(PPh3){eta(2)(P,O)-keto phosphine}][PF6] (3a,b and 3'a-e), are obtained by the reactions of complexes 1 and 1' with the keto phosphines in the presence of NH4PF6. Complex 3'c is diastereoselectively obtained as the S-Ru,R-C/R-Ru,S-C enantiomeric pair, as shown by an X-ray crystal structure analysis. Owing to the hemilabile ability of the keto phosphine ligand, complexes 3a and 3'a easily react with 1,1-diphenyl-2-propyn-1-ol to yield the allenylidene complexes [Ru(=C=C=CPh2)(eta(5)-CnHm)(PPh3){eta(1)(P)Ph2PCH2C(=O)Bu-t}][PF6] (5a and 5'a, respectively). Treatment of complexes 3a and 3'a with K2CO3 in methanol leads to the deprotonation of the coordinated keto phosphine to give the neutral phosphino enolate derivatives [Ru(eta(5)-CnHm)(PPh3){eta(2)(P,O)-Ph2PCH=C(Bu-t)O}] (6a and 6'a, respectively). In contrast, allenylidene complexes 5a and 5'a react with K2CO3 or KOH in methanol to afford the alkynyl complexes [Ru{C=CC(OMe)Ph-2}(eta(5)-CnCm)(PPh3){eta(1)(P)-Ph2PCH2C(=O)Bu-t}] (7a and 7'a), which are formed through the nucleophilic addition of the methoxy group to the C-gamma atom of the allenylidene chain. Similarly, the ethoxy alkynyl derivative 8a is obtained by the reaction of Sa with KOH in ethanol. Under mild basic conditions (K2CO3/THF)) complexes 5a and 5'a are deprotonated, resulting in conversion into the neutral derivatives [Rut {eta(2)(C,P)-C(=C=CPh2)CH[C(=O)Bu-t]PPh2](eta(5)-CnHm)(PPh3)] (9a and 9'a, respectively) through the generation of a novel phosphametallacyclobutane ring and in accord with a diastereoselective process. The molecular structure of 9'a, determined by an IC-ray crystal structure analysis, discloses a S-Ru,R-C/R-Ru,S-C configuration and shows a nearly planar Ru-P(2)-C(2B)-C(1) ring bearing an almost linear eta(1)(C)-coordinated allenyl group (C(1)-C(2A)-(3A) = 169.6(8)degrees). The formation of the four-membered ring probably takes place in a putative intermediate arising from the deprotonation of the eta(1)(P)-keto phosphine ligand in 5a and 5'a. The subsequent intramolecular carbon-carbon bond formation between the allenylidene group and the nucleophilic eta(1)(P)-phosphino enolate ligands is geometrically constrained to occur at the electrophilic C-alpha site of the allenylidene ligand, and the ruthenium fragment efficiently directs the configuration of the new stereogenic carbon atom in the resulting metallacycle ring.