INTRAMOLECULAR C-C BOND FORMATION FROM b-KETO PHOSPHINE AND ALLENYLIDENE LIGANDS IN RELATED RUTHENIUM(II) CYCLOPENTADIENYL AND INDENYL COMPLEXES. X-RAY CRYSTAL STRUCTURE STUDY

J. Borge & S. García-Granda

Departamento de Química Física y Analítica. Facultad de Química. Universidad de Oviedo. C/ Julián Clavería, 8. 33006 Oviedo. Spain. Email: jjba@sauron.quimica.uniovi.es

The reaction of b-ketophosphines Ph₂PCH(R')C(=O)R [a: R = Bu^t, R' = H; b: R = Ph, R' = H; c: R = Bu^t, R' = Me] with [RuCl(h⁵-CnHm)(PPh₃)₂] complexes [1, C_nH_m = cyclopentadienyl; 1', C_nH_m = indenyl] affords neutral [RuCl(h⁵-C_nH_m)(PPh₃){h¹-(P)-ketophosphine}], 2a,b and 2'a. Cationic derivatives. [Ru(h⁵-C_nH_m)(PPh₃){h²-(P,O)-ketophosphine}][PF₆], 3a,b and 3'a-c, are obtained by the reactions of complexes 1 and 1' with the ketophosphines in the presence of NH₄PF₆. Complex 3'c is diastereoselectively obtained as the S_RuR_C/R_RuS_C enantiomeric pair as shown by an X-ray crystal structure analysis. Owing to the hemilabile ability of the ketophosphine 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)(h⁵-C_nH_m)(PPh₃){h¹-(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 ketophosphine to give the neutral phosphino-enolate derivatives [Ru(h⁵-C_nH_m)(PPh₃){h²-(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)Ph₂}(h⁵-C_nH_m)(PPh₃){h¹-(P)-Ph₂PCH₂C(=O)Bu^t}] 7a and 7'a which are formed through the nucleophilic addition of the methoxy group to the Cg 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 to be converted into the neutral derivatives [Ru{h²-(C,P)-C(=C=CPh₂)CH[C(=O)Bu^t]PPh₂}(h⁵-C_nH_m)(PPh₃)], 9a and 9'a respectively through the generation of a novel phosphametallacyclobutane ring and according to a diastereoselective process. The molecular structure of 9'a determined by an X-ray crystal structure analysis discloses a S_RuR_C/R_RuS_C configuration and shows a nearly planar Ru-P(2)-C(2B)-C(1) ring bearing an almost linear h¹-(C)-coordinated allenyl group [C(1)-C(2A)-C(3A)= 169.6(8)º]. The formation of the four-membered ring probably takes place in a putative intermediate arising from the deprotonation of the h¹-(P)-ketophosphine ligand in 5a and 5'a. The subsequent intramolecular carbon-carbon bond formation between the allenylidene group and the nucleophilic h¹-(P)-phosphino-enolate ligands is geometrically constrained to occur at the electrophilic Ca site of the allenylidene ligand and the ruthenium fragment efficiently directs the configuration of the new stereogenic carbon atom in the resulting metallacycle ring.

Crochet, P., Demerseman, B., Vallejo, M. I., Gamasa, M. P., Gimeno, J., Borge, J. & García-Granda, S. (1997). Organometallics 16, 5406-5415.