Syntheses and Chemistry of the Diynyl Complexes M(C⋮CC⋮CH)(CO)₃(η-C₅H₅) (M = Mo, W):  Crystal Structures of W(C⋮CC⋮CSiMe₃)(CO)₃(η-C₅H₅), W{C⋮CC[CH=C(CN)₂]=C(CN)₂}(CO)₃(η-C₅H₅), and <i>cis</i>-W(C⋮CPh)(CO)₂(PPh₃)(η-C₅H₅)

Reactions of buta-1,3-diyne with appropriate metal halides, carried out in the presence of CuI in NHEt₂, have given high yields of M(C⋮CC⋮CH)(CO)<i>_n</i>Cp [M = W (<b>1-W</b>), Mo (<b>1-Mo</b>), <i>n</i> = 3; M = Fe, <i>n</i> = 2 (<b>2</b>)]. Complex <b>1-W</b> was metalated with LiNPrⁱ₂; subsequent reactions with SiClMe₃ or PClPh₂ gave W(C⋮CC⋮CR)(CO)₃Cp [R = SiMe₃ (<b>3</b>) or P(O)Ph₂ (<b>4</b>)] in modest to high yield. Coupling of <b>1</b> with iodoarenes, catalyzed by a mixed Cu^I−Pd⁰ catalyst, gave M(C⋮CC⋮CAr) (CO)₃Cp [M = W, Ar = Ph (<b>5-W</b>), tol (<b>6</b>), C₆H₄OMe-4 (<b>7</b>), C₆H₄CO₂Me-4 (<b>8</b>); M = Mo, Ar = Ph (<b>5-Mo</b>)]. Oxidative coupling of <b>1</b> (CuCl-tmed-O₂) gave {M(CO)₃Cp}₂(μ-C₈) [M = W (<b>9-W</b>), Mo (<b>9-Mo</b>)]. Addition of tetracyanoethene to <b>1-W </b>occurred at the C⋮C triple bond further from the metal atom, to give W{C⋮CC[=C(CN)₂]CHC(CN)₂}(CO)₃Cp (<b>10</b>). Substitution of CO by PPh₃ was difficult, but the Me₃NO-induced reaction with <b>5-W</b> afforded <i>cis</i>-W(C⋮CC⋮CPh)(CO)₂(PPh₃)Cp (<b>11</b>) in low yield. The X-ray crystal structures of <b>3</b> and <b>10</b>, together with that of <i>cis</i>-W(C⋮CPh)(CO)₂(PPh₃)Cp (<b>12</b>), are reported.