The 62-electron cluster [Ru 4 (CO) 13 (µ 3 -PPh)] (1) reacts with phosphalkynes RCtP [(R ) tBu, Ar′ (2,4,6-tBu 3 C 6 H 2 )] to yield a series of unsymmetrically capped bisphosphinidene clusters characterized by a ketene substituted µ 4 -PR ligand. The reaction pathway was followed by 31 P-NMR spectroscopy and reveals that, in the first step of the reaction, a CO substitution of 1 occurs in order to form an intermediate with a σ-or π-bonded phosphaalkyne. After scavenging of CO the chain compound [Ru 4 (CO) 12 (µ 3 -PPh)(µ 3 -PC(CO)R)] [R ) tBu (2), Ar′ ( 7)] is created. Further CO elimination leads to the closo-complexes [Ru 4 (CO) 10 (µ-CO)-(µ 4 -PPh)(µ 4 -PC(CO)R)] [R ) tBu (3), Ar′ (4)]. Due to steric reasons the nido-cluster [Ru 3 (CO) 9 (µ 3 -PPh){µ 3 -PC(CO)tBu}] (5) is the final product in the reaction starting from Ar′CtP. The molecular structures of the complexes 2-5 are discussed.1 provides an opportunity to explore the chemistry of RCtP on cluster frames, and our findings are presented herein. Results and DiscussionThe reactions of [Ru 4 (CO) 13 (µ 3 -PPh)] (1) with different phosphaalkynes lead to various ketene ligand-containing clusters. The ligand tBuCtP reacts with 1 at ambient temperatures to yield the complex [Ru 4 (CO) 12 -(µ 3 -PPh)(µ 3 -PC(CO)tBu)] (2) (Scheme 1), whereas at 60 °C the closo-complex [Ru 4 (CO) 10 (µ-CO)(µ 4 -PPh)(µ 4 - † Dedicated to Professor W. Siebert on the occasion of his 60th birthday.