The reactions of [RuClH(CO)(PPh3)3] and [RuH(CO)(NCMe)2(PPh3)2]ClO4 with [NMe4][B3H8] provide the ruthenatetraborane [RuH(B3H8)(CO)(PPh3)2] [Crystallographically characterized: monoclinic crystals of space group P2(1)/c (Z = 4), in a unit cell of dimensions a = 14.424 (5) angstrom, b = 10.628 (4) angstrom, c = 22.987 (9) angstrom, and beta = 97.86 (3)-degrees]. The integrity of the RuB3 moiety is retained in the reactions with N-halosuccinimides, leading to the halo derivatives [RuX(B3H8)(CO)(PPh3)2] (X = Cl, Br, 1); however, reaction of the bromo derivative with Na[S2CNMe2] leads to rupture of the metallatetraborane and formation of [Ru(S2CNMe2)2(CO)(PPh3)].