Alkyne/Methylene Coupling Reactions at Adjacent Rh/Os Centers:  Stepwise Transformations from C₁- through C₄-Bridged Species

Abstract

Reaction of the methylene-bridged complex [RhOs(CO)3(μ-CH2)(dppm)2][CF3SO3] (dppm = μ-Ph2PCH2PPh2) with dimethyl acetylenedicarboxylate or hexafluorobutyne results in alkyne insertion into the Rh−CH2 bond, yielding [RhOs(CO)3(μ-η1:η1-RCC(R)CH2)(dppm)2][CF3SO3] (R = CO2Me (5), CF3 (6)). Carbonyl removal from each of these species results in a Rh-bound carbonyl being replaced by a triflate ion. Reaction of 5 with diazomethane results in CH2 insertion into the Rh−C(R) bond with accompanying C−H activation of the original osmium-bound CH2 group, yielding [RhOs(CO)3(μ-η1:η1-CH2C(R)C(R)CH)(μ-H)(dppm)2][CF3SO3] (R = CO2Me). Reaction of the alkyne-bridged species [RhOs(CO)3(μ-η1:η1-RCCR)(dppm)2][CF3SO3] (R = CO2Me) with diazomethane at −78 °C yields [RhOs(CO)3(μ-η1:η1-CH2C(R)CR)(dppm)2][CF3SO3] (12), which upon warming to ambient temperature, in the absence of diazomethane, undergoes alkyne deinsertion to yield [RhOs(CO)3(η2-RC⋮CR)(μ-CH2)(dppm)2][CF3SO3] (13). This species and the inserted product (12) appear to be in equilibrium, so reaction of 13 with diazomethane proceeds via 12 to give [RhOs(CO)3(η1:η1-CH2CH2C(R)CR)(dppm)2][CF3SO2] (14), in which the hydrocarbyl fragment is chelating to Os and interacting with Rh via an agostic interaction with one of the Os-bound CH2 hydrogens. Upon standing for weeks, or more rapidly upon refluxing, compound 14 transforms into an isomer (15) in which the C4 unit has migrated from sites on Os adjacent to Rh to sites on Os remote from Rh. An X-ray structure determination of compound 15 as the BF4 - salt confirms the geometry of this final species. Reaction of the hexafluorobutyne-bridged species [RhOs(CO)3(μ-η1:η1-RCCR)(dppm)2][CF3SO3] (R = CF3) with diazomethane does not give a product analogous to that described for dimethyl acetylenedicarboxylate, but yields the isomer 6. These carbon−carbon bond forming processes are discussed.

Reactions of nickel-group 6 complexes with a bulky terminal alkyne to afford alkyne–carbonyl coupled products: X-ray structure of the heterobimetallic nickelacyclobutenone complex [(η5-C5Me5)Mo(CO)2(η5-C5H4Me)] (Ni–Mo)

“…The spectroscopic data of all three products were similar (see Section 3.1) and indicated that complexes 3 had similar structures. The spectroscopic data of complex 3c are discussed here and are consistent with the structure [Cp*Ni{µ-η 1 ,η 3 -C(H)=C(R)-C(O)}Mo(CO) 2 Cp'] (Ni-Mo) shown in Fig. 2.…”

“…Many research groups have been interested in alkyne reactions with mixed metal complexes, in particular those that involve carbon-carbon coupling [1][2][3][4][5][6]. We share these interests and have been studying the reactions of [Cp aNi(CO)-M(CO) 3 Cp b ] (M = Cr, Mo, W; Cp a = Cp, Cp * ; Cp b = Cp, Cp 0 ) 1 and, more recently, of the unsaturated tricarbonyl complexes 1 [Cp * Ni@M(CO) 3 Cp ] (Cp = Cp, Cp 0 ; M = Mo, W) [7] with alkynes [8][9][10][11][12][13][14][15][16].…”

“…The synthesis and some reactions of the carbocationic complexes [CpNi(l-g 2 ,g 2 -HC 2 CMe 2 )M-(CO) 2 Cp 0 ] + (Ni-M: 2a, M = Mo; 2b, M = W) were recently described. The nickel-molybdenum cation is formed by the protonation of an alkoxy-alkyne complex; subsequent loss of methanol, as shown in Scheme 2 affords complex 2a [15].…”

Carbene insertion into transition metal–carbon bonds: a new tool for catalytic C–C bond formation

“…88 Further information was obtained by adding diazomethane to vinylidene-bridged species (Scheme 26). This leads to similar types of carbene insertion reactions with a comparable temperature dependency, 91 and shows that carbene insertion into bridging positions is possible. Alkyl ligand migration between the two metals apparently plays an important role.…”

Construction of a Functionalized Selenophene‐Allylidene Ligand via Alkyne Double Action at a Diiron Complex

“…The insertion of (electron‐poor) alkynes into metal‐µ‐alkylidene bonds aroused attention due to its relevance to the C–C chain growth in the Fischer–Tropsch process, and has been documented with complexes based on the [M 2 Cp 2 (CO) 2 ] skeleton (M = Fe, Ru), and Rh–Ru, Rh–Os and Ir–Os systems . In general, a vacant metal site is necessary to allow alkyne entrance through preliminary η 2 ‐coordination; both chemical and photolytic methods may be employed to this purpose,, except in the rare case that cleavage of the metal–metal linkage is feasible …”