Intramolecular C−C Bond Formation from β-Keto Phosphine and Allenylidene Ligands in Related Ruthenium(II) Cyclopentadienyl and Indenyl Complexes. X-ray Crystal Structure of (SRu,RC/RRu,SC)- [Ru(η5-C9H7)(PPh3){η2(P,O)-Ph2PCH(Me)C(But)O}][PF6] and (SRu,RC/RRu,SC)- [Ru{η2(C,P)-C(CCPh2)CH[C(O)But]PPh2}(η5-C9H7)(PPh3)

Abstract

The reaction of β-keto phosphines Ph2PCH(R‘)C(O)R (a, R = But, R‘ = H; b, R = Ph, R‘ = H; c, R = But, R‘ = Me) with [RuCl(η5-CnHm)(PPh3)2] complexes (1, CnHm = cyclopentadienyl; 1‘, CnHm = indenyl) affords neutral [RuCl(η5-CnHm)(PPh3){η1(P)-keto phosphine}] (2a,b and 2‘a). Cationic derivatives, [Ru(η5-CnHm)(PPh3){η2(P,O)-keto phosphine}][PF6] (3a,b and 3‘a−c), 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 SRu,RC/RRu,SC 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(CCCPh2)(η5-CnHm)(PPh3){η1(P)-Ph2PCH2C(O)But}][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(η5-CnHm)(PPh3){η2(P,O)-Ph2PCHC(But)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)Ph2}(η5-CnHm)(PPh3){η1(P)-Ph2PCH2C(O)But}] (7a and 7‘a), which are formed through the nucleophilic addition of the methoxy group to the Cγ atom of the allenylidene chain. Similarly, the ethoxy alkynyl derivative 8a is obtained by the reaction of 5a with KOH in ethanol. Under mild basic conditions (K2CO3/THF) complexes 5a and 5‘a are deprotonated, resulting in conversion into the neutral 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 X-ray crystal structure analysis, discloses a SRu,RC/RRu,SC configuration and shows a nearly planar Ru−P(2)−C(2B)−C(1) ring bearing an almost linear η1(C)-coordinated allenyl group (C(1)−C(2A)−(3A) = 169.6(8)°). The formation of the four-membered ring probably takes place in a putative intermediate arising from the deprotonation of the η1(P)-keto phosphine ligand in 5a and 5‘a. The subsequent intramolecular carbon−carbon bond formation between the allenylidene group and the nucleophilic η1(P)-phosphino enolate ligands is geometrically constrained to occur at the electrophilic Cα site of the allenylidene ligand, and the ruthenium fragment efficiently directs the configuration of the new stereogenic carbon atom in the resulting metallacycle ring.