STUDY ON ISOLOBAL REACTIONS IN TRANSITION-METAL CLUSTER SYSTEMS - SYNTHESIS OF HETERONUCLEAR METAL CLUSTER COMPLEXES (ETA(5)-C5H5)(ETA(5)-RC5H4)MONIFE2S(CO)(10), -C5H5)MONIFE2S(CO)(10)](2)[ETA(5)-C5H4C(O)CH2](2), ES(CO)(5)][MOCOFES(CO)(8)][ETA(5)-C5H4C(O)CH2](2), AND (5)-C5H5)MONIFES(CO)(5)](2)[ETA(5)-C5H4C(O)CH2](2)

Reactions of the single-tetrahedral MoNiFeS clusters (eta(5)-C5H5)(eta (5)-RC5H4)Mo NiFeS(CO)(5) [R = H (1), MeCO (2), MeO2C (3)] with Fe-2(C O)(9) in toluene at 45-50 degrees C gave an isolobal displacement/addi tion type of products (eta(5)-C5H5)(eta(5)-RC5H4)MoNiFe2S(CO)(10) [R = H.(4), MeCO (5), MeO2C (6)], whereas the double-tetrahedral MoNiFeS c luster 5)-C5H5)MoNiFeS(CO)(5)](2)-[eta(5)-C5H4C(O)CH2](2) (7) reacted with Fe-2(CO)(9) under similar conditions to give the same type of rea ction product )-C5H5)MoNiFe2S(CO)(10)](2)[eta(5)-C5H4C(O)CH2](2) (8). In contrast to the chemical behavior of such tetrahedral clusters, the tetrahedral MoCoFeS cluster [MoCoFeS(CO)(8)](2)[eta(5)-C5H4C(O)CH2](2 ) (9) reacted with Cp2Ni in refluxing THF to afford only the isolobal displacement type of products (5)-C5H5)MoNiFeS(CO)(5)](2)[eta(5)-C5H4C (O)CH2](2) (7) and FeS(CO)(5)][MoCoFeS(CO)(8)][eta(5)-C5H4C(O)CH2](2) (10) The X-ray molecular structures of 5 and 7 are described, and a po ssible pathway for the novel reaction yielding the isolobal displaceme nt/addition type of products has been briefly discussed.