Comparative Bonding Behavior of Functional Cyclopentadienyl Ligands and Boron-Containing Analogues in Heterometallic Complexes and Clusters^†

The reactivity of isolobal molybdenum carbonylmetalates containing a 2-boratanaphthalene, [Mo(η⁵-2,4-MeC₉H₆BMe)(CO)₃]^- (5a) and [Mo(η⁵-2,4-MeC₉H₆BNi-Pr₂)(CO)₃]^- (5b), a 1-boratabenzene, [Mo(η⁵-3,5-Me₂C₅H₃BNi-Pr₂)(CO)₃]^- (8), or a functionalized cyclopentadienyl ligand, the new metalate [Mo(η⁵-C₅H₄Ph)(CO)₃]^- (7) and [Mo(η⁵-C₅H₄NMe₂)(CO)₃]^- (9), toward palladium (I and II) or platinum (I and II) complexes, such as trans-[PdCl₂(NCPh)₂], [Pd₂(NCMe)₆](BF₄)₂, trans-[PtCl₂(PEt₃)₂], and [N(n-Bu)₄]₂ [Pt₂Cl₄(CO)₂], has been investigated, and this has allowed an evaluation of the influence of the π-bonded ligands on the structures and unprecedented coordination modes observed in the resulting metal−metal-bonded heterometallic clusters. The new 58 CVE planar-triangulated centrosymmetric clusters, [Mo₂Pd₂(η⁵-C₅H₄Ph)₂(CO)₆(PEt₃)₂] (11), [Mo₂Pd₂(η⁵-2,4-MeC₉H₆BNi-Pr₂)₂(CO)₆] (12), [Mo₂Pd₂(η⁵-3,5-Me₂C₅H₃BNi-Pr₂)₂(CO)₆] (13), [Mo₂Pd₂(η⁵-C₅H₄NMe₂)₂(CO)₆(PEt₃)₂] (15), [Mo₂Pt₂(η⁵-C₅H₄NMe₂)₂(CO)₆(PEt₃)₂] (16), and [Mo₂Pt₂(η⁵-C₅H₄NMe₂)₂(CO)₈] (20), have been characterized by single-crystal X-ray diffraction. Their structural features were compared with those of the 54 CVE cluster [Re₂Pd₂(η⁵-C₄H₄BPh)₂(CO)₆)] (4), previously obtained from the borole-containing metalate [Re(η⁵-C₄H₄BPh)(CO)₃]^- (2), in which a 2e−3c B−C_ipso−Pd interaction involving the π-ring was observed. As an extension of what has been observed in 4, clusters 12 and 13 present a direct interaction of the boratanaphthalene (12) and the boratabenzene (13) ligands with palladium. In clusters 11, 15, 16, and 20, the π-ring does not interact with the palladium (11 and 15) or platinum centers (16 and 20), which confers to these clusters a geometry very similar to that of [Mo₂Pd₂(η⁵-C₅H₅)₂(CO)₆(PEt₃)₂] (3b). The carbonylmetalates [Mo(π-ring)(CO)₃]^- are thus best viewed as formal four electron donors which bridge a dinuclear d⁹−d⁹ unit. The orientation of this building block in the clusters influences the shape of their metal cores and the bonding mode of the bridging carbonyl ligands. The crystal structure of new centrosymmetric complex [Mo(η⁵-C₅H₄Ph)(CO)₃]₂ (10) was determined, and it revealed intramolecular contacts of 2.773(4) Å between the carbon atoms of carbonyl groups across the metal−metal bond and intermolecular bifurcated interactions between the carbonyl oxygen atoms (2.938(4) and 3.029(4) Å), as well as intermolecular C−H···π_Ar(CC) interactions (2.334(3) and 2.786(4) Å) involving the phenyl substituents.