(Eta6-naphthalene)Mn(CO)(3)(+) is reduced reversibly by two electrons in CH(2)Cl(2) to afford (eta4-naphthalene)Mn(CO)(3)(-). The chemical and electrochemical reductions of this and analogous complexes containing polycyclic aromatic hydrocarbons (PAH) coordinated to Mn(CO)(3)(+) indicate that the second electron addition is thermodynamically easier but kinetically slower than the first addition. Density functional theory calculations suggest that most of the bending or folding of the naphthalene ring that accompanies the eta6 --> eta4 hapticity change occurs when the second electron is added. As an alternative to further reduction, the 19-electron radicals (eta6-PAH)Mn(CO)(3) can undergo catalytic CO substitution when phosphite nucleophiles are present. Chemical reduction of (eta6-naphthalene)Mn(CO)(3)(+) and analogues with one equivalent of cobaltocene affords a syn-facial bimetallic complex (eta4,eta6-naphthalene)Mn(2)(CO)(5), which contains a Mn-Mn bond. Catalytic oxidative activation under CO reversibly converts this complex to the zwitterionic syn-facial bimetallic (eta4,eta6-naphthalene)Mn(2)(CO)(6), in which the Mn-Mn bond is cleaved and the naphthalene ring is bent by 45 degrees . Controlled reduction experiments at variable temperatures indicate that the bimetallic (eta4,eta6-naphthalene)Mn(2)(CO)(5) originates from the reaction of (eta4-naphthalene)Mn(CO)(3)(-) acting as a nucleophile to displace the arene from (eta6-naphthalene)Mn(CO)(3)(+). Heteronuclear syn-facial and anti-facial bimetallics are formed by the reduction of mixtures of (eta6-naphthalene)Mn(CO)(3)(+) and other complexes containing a fused polycyclic ring, e.g., (eta5-indenyl)Fe(CO)(3)(+) and (eta6-naphthalene)FeCp(+). The great ease with which naphthalene-type manganese tricarbonyl complexes undergo an eta6 --> eta4 hapticity change is the basis for the formation of both the homo- and heteronuclear bimetallics, for the observed two-electron reduction, and for the far greater reactivity of (eta6-PAH)Mn(CO)(3)(+) complexes in comparison to monocyclic arene analogues.

A series of alkylated benzothiophene and dibenzothiophene complexes containing a manganese tricarbonyl moiety coordinated to a carbocyclic ring have been synthesized. Reaction of these with the mild nucleophile Pt(PPh 3 ) 2 (C 2 H 4 ) leads to rapid room-temperature insertion of Pt(PPh 3 ) 2 into a C-S bond to afford metallathiacyclic complexes. With benzothiophene complexes bearing no substitutent at the 2-or at the 3-position, it is shown that initial rapid coordination of the platinum to the CdC bond in the heterocyclic ring takes place prior to insertion into the C(vinyl)-S bond. When a substituent is present at the benzothiophene 2-and/or 3-position, formation of the η 2 -(CdC) intermediate is blocked, the reaction rate slows, and insertion into the C(aryl)-S bond becomes possible or even dominant. An η 1 -S intermediate is suggested in these cases. Insertion into the C-S bond nearer the coordinated ring in dibenzothiophene complexes, even ones alkylated at the 4and/or 6-positions, occurs rapidly at rates similar to those found for alkylated benzothiphene complexes. Even the normally intractable 4,6-Me 2 DBT is "remotely activated" to rapid C-S bond cleavage by Pt(PPh 3 ) 2 when precoordinated to the Mn(CO) 3 + moiety. On the basis of observed regioselectivities, low-temperature infrared studies, and room-temperature stoppedflow kinetics, a mechanism is proposed for the insertion of platinum into precoordinated benzothiophenes and dibenzothiophenes. The palladium complex Pd(PPh 3 ) 2 (C 2 H 4 ) is capable of inserting into C-C, C-S, and C-Se bonds in coordinated biphenylene, thiophenes, and selenophenes. The X-ray structure of the biphenylene insertion product is reported. It is concluded that the metallacycles formed from Pd(PPh 3 ) 2 (C 2 H 4 ) are in general not as rapidly formed or as stable as those obtained with Pt(PPh 3 ) 2 (C 2 H 4 ). X-ray structures are reported for (η 5 -selenophene)Mn(CO) 3 + and its Pt(PPh 3 ) 2 insertion product.Supporting Information Available: Tables of atomic coordinates, bond lengths and angles, anisotropic displacement parameters, and hydrogen coordinates for [12]BF4, [14]BF4, and [16]BF4. This material is available free of charge via the Internet at http://pubs.acs.org. OM0102448

Stable bimetallic 'capped' metallocenes are formed by the reaction of Cp* 2 M (M = Fe, Ru, Os) with the manganese tricarbonyl transfer reagent [(h 6 -naphthalene)Mn(CO) 3 ] + .