The reaction of the tricarbadecaboranyl anion, 6-Ph-nido-5,6,9-C3B7H9-, with M(CO)(5)Br [M = Mn, Re] or [(eta(6)-C10H8)Mn(CO)(3)(+)]BF4-yielded the half-sandwich metallatricarbadecaboranyl analogues of (eta(5)-C5H5)M(CO)(3) [M = Mn, Re]. For both 1,1,1-(CO)(3)-2-Ph-closo-1,2,3,4-MC3B7H9 [M = Mn ( 2) and Re ( 3)], the metal is eta(6)-coordinated to the puckered six-membered open face of the tricarbadecaboranyl cage. Reactions of 2 and 3 with isocyanide at room temperature produced complexes 8-(CNBut)-8,8,8-(CO)(3)-9-Ph-nido-8,7,9,10-MC3B7H9 [M = Mn (4), Re (5)], having the cage A4-coordinated to the metal. Photolysis of 4 and 5 then resulted in the loss of CO and the formation of 1-(CNBut)-1,1-(CO)(2)-2-Ph-closo-1,2,3,4-MC3B7H9 [M = Mn, Re ( 6)], where the cage is again eta 6-coordinated to the metal. Reaction of 2 and 3 with 1 equiv of phosphine at room temperature produced the eta(6)-coordinated monosubstituted complexes 1,1(CO)(2)-1-P(CH3)3-2-Ph-closo-1,2,3,4-MC3B7H9 [M = Mn (7), Re (9)] and 1,1-(CO)2-1-P(C6H5) 3-2-Ph-closo1,2,3,4- MC3B7H9 [M = Mn (8), Re (10)]. NMR studies of these reactions at -40 degrees C showed that substitution occurs by an associative mechanism involving the initial formation of intermediates having structures similar to those of the eta(4)-complexes 4 and 5. The observed eta(6)-eta(4) cage-slippage is analogous to the eta(5)-eta(3) ring-slippage that has been proposed to take place in related substitution reactions of cyclopentadienyl-metal complexes. Reaction of 9 with an additional equivalent of P(CH3)(3) gave 8,8-(CO)(2)-8,8-(P(CH3)(3))(2)-9-Phnido-8,7,9,10- ReC3B7H9 (11), where the cage is eta(4)-coordinated to the metal. Photolysis of 11 resulted in the loss of CO and the formation of the disubstituted eta(6)-complex 1-CO-1,1-(P(CH3)(3))(2)-2-Ph-closo-1,2,3,4ReC(3)B(7)H(9) (12).