POLYNUCLEAR ACETYLIDE CHEMISTRY - ACETYLIDE TO ACETYLENE TRANSFORMATION AT A BINUCLEAR CENTER VIA C-C AND C-N BOND-FORMING REACTIONS - X-RAY STRUCTURE OF OS2(CO)6[MU-ETA-2-PARALLEL-TO-C(C(NHBU-TERT)(NET2))CPH](MU-PPH2)

Transformation of the edge-bound acetylide complex Os2(CO)6(m-»?2-C=CPh)(n-PPh2) (la) to the electron-rich parallel acetylene derivative Os2(CO)6[m-»2-||-C(CNHBut)(NEt2))CPh](m-PPh2) (4) has been achieved by treatment of la with the isonitrile CNBu\ resulting in nucleophilic attack and C-C bond formation of C„ of the acetylide, followed by addition of the secondary amine HNEt2 across the C-N multiple bond of the “carbon coordinated” isonitrile. Complex 4 exists in four isomeric forms in solution but as a single isomer in the solid state. An X-ray analysis shows that 4 crystallizes in the monoclinic space group P21/n with o = 16.174 (6) Â, b = 19.300 (8) Â, c = 11.745 (6) Â, ß = 101.30 (2)°, and Z = 4. The structure was solved and refined on the basis of 3998 observed (/ > 3σ(/)) reflections to R and Äw values of 0.038 and 0.039, respectively. In the molecular structure the two alkyne carbon atoms of a dipolar ^-i72-acetylene with phenyl and amidinium [C(NHBu MNEt;)] substituents, together with the diosmium fragment, constitute the dimetallacyclobutene Os-Os-C(R)-C(R’). The Os-Os and C-C bond lengths within this four-membered ring are 2.829 (1) and 1.37 (1) Â. Similar conversions of la (R = Ph), lb (R = Pr1), and lc (R = Bu’) to Os2(CO)6[m-»i2-C(C(NHPr’)(NHBut))CPh](^PPh2) (5a), Os2(CO)6[m-ï;2-C(C(NHPr’)(NHBut))CPri](m-PPh2) (5b), and Os^COJetM-^-CiCiNHPr^NHBu^CBu'KM-PPh.i) (5c) with CNBu1 and isopropylamine show the same reaction sequence observed for conversion of complex la to complex 4. © 1990, American Chemical Society. All rights reserved.