Reversible Displacement of Polyagostic Interactions in 16e [Mn(CO)(R(2)PC(2)H(4)PR(2))(2)](+) by H(2), N(2), and SO(2). Binding and Activation of eta(2)-H(2) trans to CO Is Nearly Invariant to Changes in Charge and cis Ligands.

Electrophilic 16e [Mn(CO)(R(2)PC(2)H(4)PR(2))(2)](+) complexes (R = Et, Ph) are synthesized by metathesis of MnBr(CO)(R(2)PC(2)H(4)PR(2))(2) with Na or Li salts of low-coordinating boron or gallium anions (e.g., [B{C(6)H(3)(3,5-CF(3))(2)}(4)](-) or [Ga(C(6)F(5))(4)] (-)).