Metallorganische Lewis-Säuren

Synthesis, isolation, and characterization of trisodium tricarbonyliridate (3-), Na3[Ir(CO)3]. Initial studies on its derivative chemistry and structural characterizations of trans-[Ir(CO)3(EPh3)2](-), E = Ge, Sn, and trans-[Co(CO)3(SnPh3)2](-1)

Reduction of Na[Ir(CO)4] by sodium metal in (Me2N)3PO, followed by treatment with liquid ammonia, provided high yields (ca. 90%) of unsolvated Na3[Ir(CO)3], a thermally stable, pyrophoric orange solid. This substance contains iridium in its lowest known formal oxidation state of -3 and has been characterized by IR spectroscopy, elemental analyses, and derivative chemistry, i.e., by its conversion to the triphenylgermyl and triphenylstannyl complexes, trans-[Ir(CO)3(EPh3)2](-), E = Ge, Sn. Single-crystal X-ray structures of the tetraethylammonium salts of these species, as well as [Co(CO)3(SnPh3)2](-), confirm the trigonal bipyramidal nature of the anions, originally predicted on the basis of their IR spectra in the carbonyl stretching frequency region. These structural characterizations provide important additional evidence for the presence of metal tricarbonyl units in Na3[M(CO)3], M = Co, Ir.

[Co(4)O(4)](4+) Cubane Core as a Brønsted Base: Preparation and Properties of [Co(4)O(3)(OH)(O(2)CR)(2)(bpy)(2)](3+) and [Co(4)O(2)(OH)(2)(O(2)CR)(2)(bpy)(2)](4+) Salts

The preparation and properties are described of complexes resulting from the mono- and diprotonation of the [Co(4)O(4)](4+) unit to give products containing [Co(4)O(3)(OH)](5+) and [Co(4)O(2)(OH)(2)](6+), respectively. Treatment of [Co(4)O(4)(O(2)CC(6)H(4)-p-OMe)(2)(bpy)(4)](2+) (bpy = 2,2'-bipyridine) in MeCN with 70% perchloric acid leads to isolation of [Co(4)O(2)(OH)(2)(O(2)CC(6)H(4)-p-OMe)(2)(bpy)(4)](ClO(4))(4) (5) in 61% yield. Treatment of [Co(4)O(4)(O(2)CC(6)H(4)-p-Me)(2)(bpy)(4)](2+) in MeCN with an acidic solution of (NH(4))(3)[Ce(NO(3))(6)] leads to isolation of [Co(4)O(3)(OH)(O(2)CC(6)H(4)-p-Me)(2)(bpy)(4)][Ce(NO(3))(6)] (6) in 96% yield. Complex 5.3MeCN.H(2)O crystallizes in monoclinic space group C2/c with (at -155 degrees C) a = 33.838(8) Å, b = 13.826(3) Å, c = 29.944(7) Å, beta = 98.84(1) degrees, and Z = 8. Complex 6.PhCN.H(2)O crystallizes in orthorhombic space group Pbca with (at -154 degrees C) a = 22.603(4) Å, b = 34.759(6) Å, c = 18.167(3) Å, and Z = 8. The complexes contain [Co(4)O(2)(OH)(2)](6+) (5) and [Co(4)O(3)(OH)](5+) (6) distorted-cubane cores, the sites of protonation being apparent by (i) the approach of ClO(4)(-) or [Ce(NO(3))(6)](3)(-) anions to within hydrogen-bonding distances (O.O approximately 2.7 Å) and (ii) the longer Co-OH(-) bond lengths compared with Co-O(2)(-) bond lengths. Peripheral ligation is provided by chelating bpy and syn,syn-bridging RCO(2)(-) groups. The Co(III) atoms are six-coordinate and approximately octahedral. Solution studies show that the diprotonated species is a strong diprotic acid analogous to H(2)SO(4); the first deprotonation goes to completion, but the monoprotonated species is a weak acid and is in equilibirium with the nonprotonated species. pH studies in aqueous solution yield a pK(a2) value of 3.15 for the second deprotonation. Electronic and (1)H NMR spectra of the diprotonated complexes in various solvents are consistent with the monoprotonated complex being the major species in solution. The combined results demonstrate that the [Co(4)O(4)](4+) core is capable of acting as a Brønsted base, undergoing either one or two protonation reactions.

Synthesis and Properties of IrRe(2)(&mgr;-H)(2)(CO)(9)(eta(5)-C(9)H(7))

The slow addition of Re(2)(&mgr;-H)(2)(CO)(8) to a solution of Ir(CO)(eta(2)-C(8)H(14))(eta(5)-C(9)H(7)) in hexane at reflux provides IrRe(2)(&mgr;-H)(2)(CO)(9)(eta(5)-C(9)H(7)) (1) in 80% yield. The molecular structure of 1 shows an IrRe(2) triangle incorporating one Ir(CO)(eta(5)-C(9)H(7)) and two Re(CO)(4) fragments. The strongly different Ir-Re distances suggest that one hydride ligand bridges one Ir-Re edge and the other hydride bridges the Re-Re edge. Low-temperature (1)H and (13)C NMR spectra are consistent with this structure; at higher temperatures a dynamic process involving migration of one hydride ligand between the two Ir-Re edges is observed. Cluster 1 is readily deprotonated with KOH/EtOH, and the resulting anion has been isolated as the PPN salt, [PPN][IrRe(2)(&mgr;-H)(CO)(9)(eta(5)-C(9)H(7))] (2). Both the (1)H and low temperature (13)C NMR spectra of 2 are consistent with a structure in which the remaining hydride ligand bridges the Re-Re edge. Variable-temperature (13)C NMR spectra indicate that 2 undergoes CO scrambling localized on the Ir-Re edges. The reaction of 1 with PPh(3) leads to IrRe(2)(&mgr;-H)(2)(CO)(8)(PPh(3))(eta(5)-C(9)H(7)) (3), which contains the phosphine on a rhenium atom, as well as to cluster fragmentation.