Correct option is D
Grubbs catalysts are a series of transition metal carbene complexes used as catalysts for olefin metathesis. Several generations of the catalyst have also been developed. Grubbs catalysts tolerate many functional groups in the alkene substrates, are air-tolerant, and are compatible with a wide range of solvents.
In Grubbs’ catalysts, tricyclohexylphosphane is chosen in preference to other PR3 ligands because its steric hindrance and strongly electron-donating properties lead to enhanced catalytic activity. The first step in the mechanism of alkene metathesis involving Grubbs’ catalysts is the dissociation of a P(C6H11)3 ligand to give a coordinatively unsaturated,14-electron species. The choice of the phosphane ligand is crucial for this initiation step: PR3 ligands that are less sterically demanding than P(C6H11)3 bind too strongly to Ru, whereas those that are more bulky than P(C6H11)3 are too labile and a stable starting complex is not formed. The activated complex now enters the catalytic cycle by binding an alkene. This may coordinate to the Ru centre either cis or trans to P(C6H11)3 (first generation catalyst) or the N-heterocyclic carbene ligand (second generation catalyst).
