The reaction of [Ru 3 (CO) 12 ] with P(o-tolyl) 2 H (molar ratio of 1 to 2) in refluxing THF afforded the electron-precise metal cluster [Ru 3 (μ-H) 2 (μ-P{o-tolyl} 2 ) 2 (CO) 8 ] (3). This reaction behavior is comparable to that using the secondary phosphane PtBu 2 H operating with the same molar ratio. As shown in earlier work, the ruthenium carbonyl reacted with an excess of PtBu 2 H under similar conditions with cluster degradation affording the coordinatively unsaturated complex [Ru 2 (μ-H)(μ-PtBu 2 )(PtBu 2 H) 2 (CO) 4 ]. We found that the reaction using similar reaction conditions with P(o-tolyl) 2 H in excess did not result in such