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The syntheses of [1,3,5-{(η²-dppe)(η⁵-C5Me5)FeC&tbd1;C-4-C6H4C&tbd1;C}3C6H3] (1) and [(η²-dppe)(η⁵-C5Me5)Fe(C&tbd1;C-1,4-C6H4C&tbd1;CPh)] (2) are reported, together with an X-ray diffraction study of 2. The linear optical spectra of these compounds reveal characteristic low-energy transitions at 430 and 436 nm, respectively, significantly red shifted in comparison to those recorded for [1,3,5-{(η²-dppe)(η⁵-C5Me5)FeC&tbd1;C}3C6H3] (3) and [(η²-dppe)(η⁵-C5Me5)FeC&tbd1;CPh] (4), respectively. Cubic nonlinear optical response data for 1, 2, and 4 are reported. Cubic molecular nonlinearities by Z-scan at 695 nm reveal an increase in nonlinearities upon introduction of the ligated metal unit and progression from linear monometallic complex to octupolar trimetallic complex. Oxidation of 1 to 1³⁺ results in a change of sign and magnitude of the imaginary (absorptive) part of the third-order nonlinearity; that is, the molecule can be electrochemically cycled between two-photon absorber and saturable absorber states.

Reaction between the tetrahedral cluster compound Mo2Ir2(CO)10(η⁵-C5H4Me)2 (1) and 2-iodo-5-(oct-1‘-ynyl)thiophene afforded the pseudooctahedral cluster Mo2Ir2{μ4-η²-Me(CH2)5C2-5-C4H2S-2-I}(CO)8(η⁵-C5H4Me)2 (17) by formal insertion of the alkyne C&tbd1;C group into the Mo−Mo bond. Similar reactions of 1 or W2Ir2(CO)10(η⁵-C5H4Me)2 (2) with heterocyclic di- or triynes afforded the related mono-, di-, or tricluster compounds [M2Ir2(CO)8(η⁵-C5H4Me)2]2{μ8-η⁴-Me(CH2)5C2-2-C4H2E-5-C2(CH2)5Me} [E = S, M = Mo (20), W (21); E = Se, M = Mo (30), W (31)], [M2Ir2(CO)8(η⁵-C5H4Me)2]2{μ8-η⁴-Me(CH2)5C2-2-C4H2S-5-(E)-CH&dbd;CH-2-C4H2S-5-C2(CH2)5Me} [M = Mo (22), W (24)], M2Ir2{μ4-η²-Me(CH2)5C2-2-C4H2S-5-(E)-CH&dbd;CH-2-C4H2S-5-C&tbd1;C(CH2)5Me}(CO)8(η⁵-C5H4Me)2 [M = Mo (23), W (25)], [M2Ir2(CO)8(η⁵-C5H4Me)2]3{μ12-η⁶-Me(CH2)5C2-2-C4H2S-5-C2-2-C4H2S-5-C2(CH2)5Me} [M = Mo (26), W (28)], and [M2Ir2(CO)8(η⁵-C5H4Me)2]2{μ8-η⁴-Me(CH2)5C2-2-C4H2S-5-C2-2-C4H2S-5-C&tbd1;C(CH2)5Me} [M = Mo (27), W (29)]. Compounds 27 and 29 correspond to the 1,2-dicluster adducts of the linear triyne Me(CH2)5C&tbd1;C-5-C4H2S-2-C&tbd1;C-2-C4H2S-5-C&tbd1;C(CH2)5Me. No 1,3-dicluster isomer was isolated from direct reaction, but the molybdenum-containing 1,3-dicluster isomer was prepared by exploiting organic reaction chemistry on precoordinated functionalized alkyne ligands. Thus, Sonogashira coupling of 17 with trimethylsilylacetylene and subsequent desilylation gave Mo2Ir2{μ4-η²-Me(CH2)5C2-5-C4H2S-2-C&tbd1;CR}(CO)8(η⁵-C5H4Me)2 [R = SiMe3 (18), H (19)]. Sonogashira coupling of 17 and 19 gave the 1,3-isomer [Mo2Ir2(CO)8(η⁵-C5H4Me)2]2{μ8-η⁴-Me(CH2)5C2-2-C4H2S-5-C&tbd1;C-2-C4H2S-5-C2(CH2)5Me} (32), as well as the homocoupling product [Mo2Ir2(CO)8(η⁵-C5H4Me)2]2{μ8-η⁴-Me(CH2)5C2-2-C4H2S-5-C&tbd1;CC&tbd1;C-2-C4H2S-5-C2(CH2)5Me} (33). The identities of 21, 29, and 31 were confirmed by single-crystal X-ray diffraction studies. Cyclic voltammetric scans for these complexes all show a reversible/quasi-reversible oxidation followed by an irreversible oxidation process. Dicluster compounds linked by one heterocycle, and tricluster compounds, show two reduction processes, whereas dicluster compounds with longer bridges reveal only one reduction process.

The “first-generation” alkynylruthenium dendrimers 1,3,5-C6H3(4-C&tbd1;CC6H4C&tbd1;C-trans-[Ru(dppe)2]C&tbd1;C-3,5-C6H3{4-C&tbd1;CC6H4C&tbd1;C-trans-[Ru(4-C&tbd1;CC6H4R)(dppe)2]}2)3 [R = H (19), NO2 (20)], containing nine dialkynylruthenium centers, have been prepared by convergent synthesis. Reaction of 3 equiv of 1-iodo-4-trimethylsilylethynylbenzene with triethynylbenzene, under Sonogashira coupling conditions, followed by deprotection with tetra-n-butylammonium fluoride affords 1,3,5-C6H3(4-C&tbd1;CC6H4C&tbd1;CH)3 (2), which is reacted with cis-[RuCl2(L)2] (L = dppe, dppm) to afford the octopolar, triruthenium dendritic cores 1,3,5-C6H3{4-C&tbd1;CC6H4C&tbd1;C-trans-[RuCl(L)2]}3 [L = dppe (5), L = dppm (6)] via the vinylidene intermediates [1,3,5-C6H3{4-C&tbd1;CC6H4CH&dbd;C-trans-[RuCl(L)2]}3](PF6)3 [L = dppe (3), L = dppm (4)]. Reaction of 5 with terminal alkynes 4-HC&tbd1;CC6H4R (R = H, NO2, NEt2) affords a series of related dialkynylruthenium zero-generation dendrimers 1,3,5-C6H3{4-C&tbd1;CC6H4C&tbd1;C-trans-[Ru(4-C&tbd1;CC6H4R)(dppe)2]}3 [R = H (7), NO2 (8), NEt2 (9)]. Reaction of 3 equiv of trans-[Ru(4-C&tbd1;CC6H4C&tbd1;CH)(C&tbd1;CPh)(dppe)2] with 1,3,5-triiodobenzene under Sonogashira coupling conditions also affords 7, together with the homo-coupled trans,trans-[(dppe)2(PhC&tbd1;C)Ru(4,4‘-C&tbd1;CC6H4C&tbd1;CC&tbd1;CC6H4C&tbd1;C)Ru(C&tbd1;CPh)(dppe)2]. The first-generation dendrimers 19 and 20 are prepared by coupling core 5 with the dendrons 1-(HC&tbd1;C)C6H3-3,5-{4-C&tbd1;CC6H4C&tbd1;C-trans-[Ru(4-C&tbd1;CC6H4R)(dppe)2]}2 [R = H (17), NO2 (18)]. Thus, reaction of 1-(Me3SiC&tbd1;C)C6H3-3,5-(4-C&tbd1;CC6H4C&tbd1;CH)2 (12), obtained from 1-iodo-3,5-dibromobenzene through a series of Sonogashira coupling and transhalogenation reactions, with cis-[RuCl2(dppe)2] affords 1-(Me3SiC&tbd1;C)C6H3-3,5-{4-C&tbd1;CC6H4C&tbd1;C-trans-[RuCl(dppe)2]}2 (13), which can be reacted with appropriately functionalized terminal alkynes to afford the series 1-(Me3SiC&tbd1;C)C6H3-3,5-{4-C&tbd1;CC6H4C&tbd1;C-trans-[Ru(4-C&tbd1;CC6H4R)(dppe)2]}2 [R = H (14), NO2 (15), NEt2 (16)]. Desilylation of 16 proceeds with decomposition; in contrast, treatment of 14 and 15 with tetra-n-butylammonium fluoride gives 17 and 18, which are coupled with 5 under basic conditions to afford the dendritic complexes 19 and 20 via in situ deprotonation of the vinylidene complex intermediates. A transmission electron micrograph of 19 supported on alumina reveals molecules that are approximately 6 nm in diameter, in agreement with molecular modeling studies.

Reaction between the tetrahedral cluster compound Mo2Ir2(CO)10(η⁵-C5H4Me)2 (1) and 1-iodo-4-(oct-1‘-ynyl)benzene afforded the pseudooctahedral cluster Mo2Ir2{μ4-η²-Me(CH2)5C2-4-C6H4I}(CO)8(η⁵-C5H4Me)2 (7). Similar reactions of 1 and W2Ir2(CO)10(η⁵-C5H4Me)2 (2) with di- and triynes afforded the related mono-, di-, and tricluster compounds [M2Ir2(CO)8(η⁵-C5H4Me)2]3{μ12-η⁶-Me(CH2)5C2-4-C6H4C2C6H4-4-C2(CH2)5Me} (M = Mo (12), W (14)), [W2Ir2(CO)8(η⁵-C5H4Me)2]2{μ8-η⁴-Me(CH2)5C2-4-C6H4C2C6H4-4-C&tbd1;C(CH2)5Me} (13), Mo2Ir2{μ4-η²-Me(CH2)5C2C6H3-3,5-[C&tbd1;C(CH2)5Me]2}(CO)8(η⁵-C5H4Me)2 (15), and [Mo2Ir2(CO)8(η⁵-C5H4Me)2]2{μ8-η⁴-[Me(CH2)5C2]2-1,3-C6H3-5-C&tbd1;C(CH2)5Me} (16). Compound 13 corresponds to the 1,2-dicluster adduct of the linear triyne Me(CH2)5C&tbd1;C-4-C6H4C&tbd1;C-4-C6H4C&tbd1;C(CH2)5Me. No 1,3-dicluster isomer was isolated from direct reaction, but the related molybdenum-containing 1,3-dicluster isomer was prepared by exploiting organic reaction chemistry on precoordinated functionalized alkyne ligands. Thus, Sonogashira coupling of 7 with Me3SiC&tbd1;CH and subsequent desilylation afforded Mo2Ir2{μ4-η²-Me(CH2)5C2-4-C6H4C&tbd1;CR}(CO)8(η⁵-C5H4Me)2 (R = SiMe3 (8), H (9)). Sonogashira coupling of 7 and 9 gave the 1,3-isomer [Mo2Ir2(CO)8(η⁵-C5H4Me)2]2{μ8-η⁴-Me(CH2)5C2-4-C6H4C&tbd1;CC6H4-4-C2(CH2)5Me} (18), as well as the homocoupling product [Mo2Ir2(CO)8(η⁵-C5H4Me)2]2{μ8-η⁴-Me(CH2)5C2-4-C6H4C&tbd1;CC&tbd1;CC6H4-4-C2(CH2)5Me} (19); the identity of the latter was confirmed by a single-crystal X-ray diffraction study. Cyclic voltammetric scans for 12−14, 18, and 19 all show a reversible/quasi-reversible oxidation followed by an irreversible oxidation process. Compounds 18 and 19 (in which clusters are linked by long unsaturated bridges) exhibit one irreversible reduction process, whereas 12−14 (in which n cluster cores are linked by a phenylene unit) show n irreversible reduction processes. Density functional calculations indicate that oxidation and reduction both proceed with retention of the pseudooctahedral core geometry but that loss of a carbonyl ligand concomitant with two-electron reduction is energetically accessible, suggesting that this accounts for the irreversibility of the reduction step.

The pseudooctahedral monocluster compounds M2Ir2(μ4-η²-R¹C2R²)(μ-CO)4(CO)4(η⁵-C5H4Me)2 (M = Mo, R² = Ph, R¹ = H (12), Ph (13), Me (14); M = W, R² = Ph, R¹ = Me (15); M = Mo, R¹ = n-hexyl, R² = C6H4-4-CHO (16), C6H4-4-CH2P(O)(OEt)2 (17)) have been prepared from reactions between the tetrahedral cluster compounds M2Ir2(CO)10(η⁵-C5H4Me)2 and the alkynes R¹C2R². Similar reactions between tetrahedral cluster precursors and di- or triynes have afforded the related compounds [M2Ir2(μ-CO)4(CO)4(η⁵-C5H4R)2]2(μ8-η⁴-R¹C2BC2R¹) (R = H, R¹ = H, B = 4-C6H4-(E)-CH&dbd;CH-4-C6H4, M = Mo (18); R = Me, R¹ = n-hexyl, B = 4-C6H4, M = Mo (19), W (20); R = Me, R¹ = n-hexyl, B = 4-C6H4-(E)-CH&dbd;CH-4-C6H4, M = Mo (22), W (23); R = Me, R¹ = n-hexyl, B = 4-C6H4-(E)-CH&dbd;CH-4-C6H4-(E)-CH&dbd;CH-4-C6H4, M = Mo (24); R = Me, R¹ = H, B = (CH2)2, M = W (27)), [Mo2Ir2(μ-CO)4(CO)4(η⁵-C5H4Me)2]3{μ12-η⁶-1,3,5-C6H3[(E)-CH&dbd;CHC6H4-4‘-C2(CH2)5Me]3} (25), and W2Ir2(μ4-η²-R¹C2R²)(μ-CO)4(CO)4(η⁵-C5H4Me)2 (R¹ = n-hexyl, R² = 4-C6H4C&tbd1;C(CH2)5Me (21); R¹ = H, R² = (CH2)2C&tbd1;CH (26)). Compounds 18−20 and 22−25 contain two or three cluster units linked by unsaturated bridges, while 27 contains two cluster units linked by a saturated bridge. Compound 22 was prepared in lower yield by coupling 16 and 17 under Emmons−Horner conditions. Structural studies of examples of mono- (15), di- (22), and tricluster (25) compounds have been undertaken. Cyclic voltammetric scans for 12−15, 19, 20, 22−24, 27 and the related cluster W2Ir2(μ4-η²-PhC2Ph)(μ-CO)4(CO)4(η⁵-C5H4Me)2 (4) have been collected. All compounds show a reversible/partially reversible oxidation, followed by an irreversible oxidation process; potentials for the former increase on replacement of tungsten by molybdenum and alkyne substituent variation Me < H < Ph. UV−vis−near-IR spectroelectrochemical studies of the first oxidation process for 12, 15, and 20 show similar spectral progressions for these mono- and dicluster compounds. The reductive cyclic voltammetric scans for 4, 12−15, 22−24, and 27 all show one irreversible reduction process; compounds 19 and 20, distinguished by possessing the shortest unsaturated bridge, show two reduction processes.

A series of new acetylide complexes of the type [Fe(η⁵-C5H5)(P&arcraise;P)(p-C&tbd1;CC6H4R)] (P&arcraise;P = DPPE (=1,2-bis(diphenylphosphino)ethane), (R)-PROPHOS (=(R)-(+)-1,2-bis(diphenylphosphino)propane), R = NO2, C6H4NO2, (Z)-C(H)&dbd;C(H)C6H4NO2, (E)-C(H)&dbd;C(H)C6H4NO2) have been synthesized by halide abstraction from the precursors [Fe(η⁵-C5H5)(P&arcraise;P)(I)] and fully characterized. Quadratic hyperpolarizabilities (β) for the complexes have been determined by hyper-Rayleigh scattering at 1064 nm. The influence on the nonlinear response of acetylide chain length in proceeding from 4-nitrophenylethynyl to 4-nitrobiphenylethynyl and 4-nitro-(E)-stibenylethynyl has been studied, revealing values of the first hyperpolarizabilities among the highest reported for organometallic molecular materials. Comparisons on the nonlinear efficiencies are drawn with the related well-known families of compounds [Ru(η⁵-C5H5)(PR3)2(p-C&tbd1;C−(aryl)−NO2)] and [Fe(η⁵-C5H5)(P&arcraise;P)(p-N&tbd1;C−(aryl)−NO2)]⁺. Cubic hyperpolarizabilities (γ) determined by Z-scan at 800 nm are consistent with an increase in γ upon replacing Ru by the more easily oxidizable Fe and upon chain-lengthening the delocalizable π-bridging unit (proceeding from 4-C6H4 to (E)-4,4‘-C6H4CH&dbd;CHC6H4). X-ray crystallographic structures of complexes [Fe(η⁵-C5H5)(DPPE)(p-C&tbd1;CC6H4NO2)] and [Fe(η⁵-C5H5)(DPPE)((E)-p-C&tbd1;CC6H4C(H)&dbd;C(H)C6H4NO2)] were studied in order to investigate the existence of π-back-donation suggested by spectroscopic and electrochemical data. Crystal packing was analyzed with the aim of assessing the alignment of the molecules in the lattice and hence suggesting the magnitude of NLO properties at the macroscopic level.

The syntheses of trans-[Ru(C&dbd;CHR)Cl(pp)2]PF6 (pp = dppm, R = 4-C6H4C&tbd1;CPh, 4-C6H4CHO, 4,4‘-C6H4C&tbd1;CC6H4NO2, (E)-4,4‘-C6H4CH&dbd;CHC6H4NO2, 4,4‘,4‘ ‘-C&tbd1;CC6H4C&tbd1;CC6H4C&tbd1;CC6H4NO2; pp = dppe, R = 4-C6H4CHO, (E)-4,4‘-C6H4CH&dbd;CHC6H4NO2) and trans-[Ru(C&tbd1;CR)Cl(pp)2] (pp = dppm, R = 4-C6H4C&tbd1;CPh, 4-C6H4CHO, 4,4‘-C6H4C&tbd1;CC6H4NO2, (E)-4,4‘-C6H4CH&dbd;CHC6H4NO2, 4,4‘,4‘ ‘-C&tbd1;CC6H4C&tbd1;CC6H4C&tbd1;CC6H4NO2; pp = dppe, R = 4-C6H4CHO, (E)-4,4‘-C6H4CH&dbd;CHC6H4NO2) are reported, together with X-ray structural studies of trans-[Ru(C&tbd1;CR)Cl(pp)2] (pp = dppm, R = 4-C6H4C&tbd1;CPh; pp = dppe, R = 4-C6H4CHO, (E)-4,4‘-C6H4CH&dbd;CHC6H4NO2). Cyclic voltammetric, linear optical, and quadratic and cubic nonlinear optical response data for these new complexes, together with the corresponding data for the previously reported trans-[Ru(C&dbd;CHR)Cl(pp)2]PF6 (pp = dppm, R = Ph, 4-C6H4NO2; pp = dppe, R = Ph, 4-C6H4NO2) and trans-[Ru(C&tbd1;CR)Cl(pp)2] (pp = dppm, R = Ph, 4-C6H4NO2, (E)-4,4‘-C6H4CH&dbd;CHC6H4NO2; pp = dppe, R = Ph, 4-C6H4NO2), are reported. Oxidation potentials for the Ru^II/III couple increase on proceeding from the neutral alkynyl complex to the analogous cationic vinylidene complex and on introduction of an acceptor group (CHO or NO2); the complexes with 4-C&tbd1;CC6H4NO2 ligands are the most difficult to oxidize. In some instances, the Ru^III/IV and Ru^I/II processes have been identified together with, where relevant, nitro-centered reduction processes. The oxidized and reduced vinylidene complexes are shown to transform electrochemically into the corresponding alkynyl complexes. Optical absorption maxima undergo a red shift upon increase of acceptor strength, replacement of the coligand dppm with dppe, and replacement of the alkynyl ligand yne linkage with an ene linkage. Proceeding from the vinylidene complex to an analogous alkynyl complex results in a small red shift in absorption maximum and a significant increase in extinction coefficient. Quadratic molecular nonlinearities by hyper-Rayleigh scattering measurements at 1064 nm increase upon introduction of ligated metal (proceeding from precursor alkyne to alkynyl or vinylidene complex), an increase in acceptor strength (introduction of CHO or NO2), alkynyl chain lengthening (in the series [4-C&tbd1;CC6H4]n-4-NO2, proceeding from n = 1 and 2 to 3), and replacing the yne linkage with an ene linkage. Significant differences in β value for two vinylidene/alkynyl complex pairs suggest that they could function as precursors to protically switchable quadratic NLO materials at 1064 nm. Cubic molecular nonlinearities by Z-scan measurements at 800 nm are in many cases characterized by negative real and significant imaginary components, indicative of two-photon effects; nevertheless, a substantial increase in |γ| on proceeding to the largest molecule, trans-Ru(4,4‘,4"-C&tbd1;CC6H4C&tbd1;CC6H4C&tbd1;CC6H4NO2)Cl(dppm)2, is observed. An order of magnitude difference in γimag values (and therefore two-photon absorption (TPA) cross sections σ2) for vinylidene/alkynyl complex pairs suggest that they have potential as protically switchable TPA materials at 800 nm.

Bis(hydroxyalkylcyclopentadienyl)-containing mixed molybdenum−iridium clusters Mo2Ir2(CO)10{η-C5H4(CH2)xOH}2 [x = 2 (1), 10] react with alkyl or aryl 1,ω-diisocyanates OCNRNCO [R = (CH2)y (y = 4, 6, 12), trans-1,4-cyclohexyl, or 4-C6H4CH2-4-C6H4] to form oligourethanes with transition metal clusters in the oligomer backbone. Characterization of the cluster-containing oligourethanes is aided by spectral comparison with model cluster diurethanes Mo2Ir2(CO)10{η-C5H4(CH2)2OC(O)NHRH}2 [R = (CH2)y [y = 4 (6), 6, 12], trans-1,4-cyclohexyl] prepared from reaction between the cluster diol 1 and alkyl isocyanates HRNCO. The precursor diol cluster 1 and cluster diurethane 6 have been characterized by single-crystal X-ray diffraction studies. The extent of polymerization has been assessed by gel permeation chromatography, with little dependence on diisocyanate precursor linker R but strong dependence on alkylcyclopentadienyl linker length (CH2)x, suggesting that the steric influence of the bulky dimolybdenum−diiridium cluster core and co-ligands is the most important factor governing extent of polymerization. Supporting this assessment, the considerably more sterically hindered precursor 2-butyn-1,4-diol-substituted cluster Mo2Ir2{μ4-η²-C2(CH2OH)2}(CO)8(η-C5H5)2 fails to react to any significant extent with 1,6-diisocyanatohexane.

The reactions of Q[Au(acac)2] (Q = N(PPh3)2 (PPN; a), NPr4 (b); acac = acetylacetonato) with terminal alkynes of the type HC&tbd1;CC6H4R-4 in a 1:2 molar ratio affords the complexes Q[Au(C&tbd1;CC6H4R-4)2] (R = NO2 (1), C6H4NO2-4 (2), (E)-CH&dbd;CHC6H4NO2-4 (3)). The same alkynes react with [AuCl(CNBu^t)] in NEt3 to give the complexes [Au(C&tbd1;CC6H4R-4)(CNBu^t)] (R = NO2 (4), C6H4NO2-4 (5), (E)-CH&dbd;CHC6H4NO2-4 (6)). When NHEt2 is used instead of NEt3, attack of the secondary amine at the isonitrile ligand takes place and alkynyl carbene complexes of the type [Au(C&tbd1;CC6H4R-4){C(NHBu^t)(NEt2)}] (R = NO2 (7), C6H4NO2-4 (8), (E)-CH&dbd;CHC6H4NO2-4 (9)) are obtained. The crystal structures of 1a, 4, 7, and 9 have been determined. The cubic hyperpolarizabilities of 1a,b, 4−6, 8, 9, and the related complexes [Au(C&tbd1;CC6H4R-4)(PPh3)] (R = H (10), NO2 (11), 4-C6H4NO2 (12), (E)-CH&dbd;CHC6H4NO2-4 (13), C&tbd1;CC6H4NO2-4 (14), (Z)-CH&dbd;CHC6H4NO2-4 (15), (E)-N&dbd;CHC6H4NO2-4 (16)) have been determined by Z-scans at 800 nm. An increase in γreal is observed on replacing the coligand Bu^tNC by PPh3 (proceeding from 5 to 12 and from 6 to 13), introduction of the NO2 group (proceeding from 10 to 11), extending the arylalkynyl π-bridge (proceeding from 11 to 12−15), and replacing (Z)-CH&dbd;CH by the (E)-CH&dbd;CH linking unit (proceeding from 15 to 13).

Reactions of Cp2W2Ir2(CO)10 (1) with n equivalents of PPh3 and PMe3 (n = 1, 2) proceed in dichloromethane at room temperature to afford the clusters Cp2W2Ir2(μ-CO)3(CO)7-n(PPh3)n (n = 1 (2), 2 (3)) and Cp2W2Ir2(μ-CO)3(CO)7-n(PMe3)n (n = 1 (4), 2 (5)), respectively, in reasonable yields (38−63%). These products exhibit ligand fluxionality in solution, resolvable at low temperature into the constituent interconverting isomers. A structural study of one isomer of 2, namely 2a, reveals that the three edges of a WIr2 face of the tetrahedral core are spanned by bridging carbonyls and that the iridium-bound PPh3 ligates axially and the tungsten-bound cyclopentadienyl ligands coordinate apically and axially with respect to the plane of bridging carbonyls. Information from this crystal structure and ¹³C and ³¹P NMR spectral data have been employed to assign coordination geometries for the isomers of 2−5. NMR studies included development and use of 2D triple-resonance experiments with carbonyl cluster complexes; these ¹H−³¹P−¹³C correlation experiments, designed to elucidate P−C coupling networks involving phosphorus and carbonyl ligands (a “HPCO experiment”), benefit from the sensitivity enhancement gained from using proton detection. All the isomers of clusters 2−5 contain a carbonyl-bridged WIr2 basal plane and an apical tungsten atom; ligands can be approximately coplanar (radial) to the basal plane or below the plane (axial). The configuration of 2a (axial phosphine, axial Cp, apical Cp), as assigned by NMR spectroscopy, is consistent with the structural determination. A second configuration (2b, 4b:  axial phosphine, axial Cp, apical Cp) is the only one identified (within the temperature range 183−293 K) for the PMe3-substituted cluster 4. Two isomers, both with radial phosphine, axial phosphine, axial Cp, apical Cp configurations, have been identified for 5, namely 5a and 5b; it is likely that isomers of 3 adopt the same configurations. The WIr2-bridged form is seen exclusively across the isomers, indicating that the presence of two electropositive tungsten atoms may be polarizing the electron distribution toward the iridiums, although steric factors may also be involved.

The impact upon ligand coordination geometry and carbonyl fluxionality of heterometal incorporation into the prototypical tetrahedral cluster Ir4(CO)12 has been assessed. The isostructural CpWIr3(CO)11 (1) is related to Ir4(CO)12 by conceptual replacement of a late transition metal-containing Ir(CO)3 vertex by a mid transition metal CpW(CO)2 unit. This “very mixed” metal cluster has been derivatized by phosphines, the ligand fluxionality of the resultant clusters has been examined, and both the coordination geometry and CO mobility of the tungsten−iridium clusters have been contrasted with those of derivatives of the “parent” homometallic cluster. The tetrahedral clusters CpWIr3(μ-CO)3(CO)8-n(L)n [L = PPh3, n = 1 (2), 2 (3); L = PMe3, n = 1 (4), 2 (5)] are shown to exist as mixtures of interconverting isomers in solution. The structures of the isomers have been assigned using a combination of variable-temperature ³¹P and ¹³C NMR, COSY spectra and X-ray structural studies. All phosphine-containing clusters contain a carbonyl-bridged basal plane and an apical metal; ligands can be approximately coplanar (radial) to the basal plane or below the plane (axial). The configurations of 2a and 4a (axial phosphine, apical Cp, Ir3 basal plane) and 2b and 4b (radial phosphine, radial or axial Cp, WIr2 basal plane) are consistent with structural determinations of 4a and 2b; a third configuration (2c; axial phosphine, radial or axial Cp, WIr2 basal plane) is observed only with the larger phosphine. The configurations of 3b and 5b (radial phosphine, axial phosphine, radial or axial Cp, WIr2 basal plane) are consistent with a structural determination of 3b, while a further configuration (3a and 5a; diradial phosphines, radial Cp, WIr2 basal plane) possesses a triradial coordination geometry. The configurations of 2a, 3a, 4a, and 5a are without precedent in monodentate ligand-substituted derivatives of the parent tetrairidium system. In contrast to reports with rhodium−iridium clusters, we find that the presence of the more electropositive tungsten does not polarize the electron distribution toward the iridiums and thereby favor an Ir3 basal plane; rather, the WIr2-bridged form is predominant across the isomers in the tungsten−iridium system. Suggested mechanisms of carbonyl fluxionality in the abundant isomers of 2−5, assigned using ¹³C exchange spectroscopy (EXSY) spectra, are proposed. Clusters 2a and 4a, with mutually trans phosphine and Cp, exchange carbonyls via a merry-go-round at Ir3 and WIr2 faces. Clusters 3a and 5a exchange all carbonyls by way of two processes:  scrambling about the Ir3 face to afford an intermediate with the carbonyl distribution of the D2d form implicated in carbonyl mobility at Ir4(CO)12, and scrambling about a WIr2 face by way of an all-terminal intermediate in which the putative merry-go-round process is blocked by phosphines and Cp.

The series of complexes Au(C&tbd1;CR)(PPh3) (R = Ph (2), 4-C6H4NO2 (3), 4,4‘-C6H4C6H4NO2 (4), (E)-4,4‘-C6H4CH&dbd;CHC6H4NO2 (5), (Z)-4,4‘-C6H4CH&dbd;CHC6H4NO2 (6), 4,4‘-C6H4C&tbd1;CC6H4NO2 (7), 4,4‘-C6H4N&dbd;CHC6H4NO2 (8)) have been synthesized by reaction of AuCl(PPh3) with the corresponding acetylene and methoxide, and complexes 3−8 have been structurally characterized. The molecular first hyperpolarizabilities for the complexes have been determined by hyper-Rayleigh scattering at 1064 nm. Introduction of the nitro substituent (in proceeding from 2 to 3) leads to a significant increase in nonlinearity. Experimental β values increase as 3 < 4 < 6 ≈ 7 < 8 < 5 consistent with nonlinearity increasing with (i) chain lengthening, (ii) replacing biphenyl (4) or yne linkage (7) by ene linkage (5), (iii) replacing (Z)-ene stereochemistry (6) with (E)-ene stereochemistry (5), and (iv) ene linkage (5) being more efficient than imino linkage (8). The same trend is observed with two-level-corrected data. A linear correlation of both experimentally-determined and two-level-corrected nonlinearities of the acetylides with precursor acetylenes is observed.

Reactions of CpWIr3(CO)11 (1) with stoichiometric amounts of phosphines afford site-selective products CpWIr3(μ-CO)3(CO)8-x(L)x (L = PPh3, x = 1 (2), 2 (3), or 3 (4); L = PMe3, x = 1 (5), 2 (6), or 3 (7)) in fair to excellent yields (38−63%). These products exhibit ligand fluxionality in solution, resolvable at low temperature into the constituent interconverting isomers. The structures of three of the species, namely 2a, 3a, and 5a, have been determined by X-ray diffraction studies. The single-crystal X-ray studies reveal that ligand substitution induces a rearrangement in the cluster coordination sphere from the all-terminal carbonyl ligand geometry of CpWIr3(CO)11 to one in which the three edges of a WIr2 face of the tetrahedral core contain bridging carbonyls (2a, 3a) or one in which the three edges of the triiridium face are bridged by carbonyl ligands (5a). The triphenylphosphine in 2a ligates radially to the carbonyl-bridged WIr2 face; a similar site for one of the phosphines is found in 3a, with the second triphenylphosphine coordinated in an axial position with respect to this face. The trimethylphosphine ligand in 5a is located in an axial site with respect to the basal carbonyl-bridged triiridium plane. Information from the crystallographically-verified isomers, the ligand substitution pattern in the related tetrairidium system, and chemical shifts of signals in the ³¹P NMR spectra has been used to suggest coordination geometries for the isomeric forms of the complexes above and for other reported derivatives.

The reaction of (benzyne)nickel(0) complexes Ni(η²-C6H4)(dcpe) (1) and Ni((1,2-η)-4,5-F2C6H2)(dcpe) (2) [dcpe = 1,2-bis(dicyclohexylphosphino)ethane, (C6H11)2PCH2CH2P(C6H11)2] with carbon monoxide at low concentration gives Ni(CO)2(dcpe) (3) and, as the main organic products, 9H-fluoren-9-one (4) and 2,3,6,7-tetrafluoro-9H-fluoren-9-one (5), 2,3,6,7-X4C12H4CO (X = H, F), respectively, resulting from monoinsertion into the nickel−benzyne bond. Higher concentrations of CO give rise to bis(acyl) intermediates, one of which, Ni(CO-4,5-F2C6H2CO-2)(dcpe) (9), has been observed by ³¹P and ¹⁹F NMR spectroscopy. These intermediates reversibly form 3 and the corresponding benzocyclobutenediones OC-4,5-X2C6H2CO [X = H (12), F (13)] by reductive elimination and react readily with oxygen to form the stable (phthalato)nickel(II) complexes Ni(OCOC6H4COO-2)(dcpe) (6) and Ni(OCO-4,5-F2C6H2COO-2)(dcpe) (7). On treatment with iodine, the latter give the corresponding phthalic anhydrides C6H4C2O3 (10) and 4,5-F2C6H2C2O3 (11), respectively. According to a single-crystal X-ray study, 7 is a planar nickel(II) complex containing a seven-membered chelate ring with monodentate carboxylato groups, the average Ni−O and Ni−P distances being 1.904(4) and 2.152(2) Å, respectively.

Reactions of Cp2W2Ir2(CO)10 (1) with terminal arylalkynes HC&tbd1;CR afford the complexes Cp2W2Ir2(μ4-η²-HC2R)(μ-CO)4(CO)4 [R = Ph (3), C6H4Me-4 (4), C6H4NO2-4 (5)] in excellent yields (56−70%). The analogous adduct with the terminal alkylalkyne HC&tbd1;CBu^t is obtained in much lower yield (20%). An X-ray structural study of 3 reveals that the alkynes have formally inserted into the W−W bond of 1, affording clusters with a pseudooctahedral geometry. The site of reactivity in 1 is consistent with the lack of reactivity towards terminal alkynes of the isostructural and isolobally related CpWIr3(CO)11 (2). Reaction of 1 with the buta-1,3-diynyl complex CpW(CO)3(C&tbd1;CC&tbd1;CH) (8) affords the analogous adduct Cp2W2Ir2{μ4-η²-HC2C&tbd1;CW(CO)3Cp)(μ-CO)4(CO)4 (9), shown spectroscopically to be attached via the C&tbd1;CH unit rather than the WC&tbd1;C group. Attempts at condensing the pendant CpW(CO)3C&tbd1;C unit with the W2Ir2 core in 9 have proven unsuccessful. Reactions of CpWIr3(CO)11 (2) with equimolar amounts of the tungsten acetylides CpW(CO)3(C&tbd1;CR) (R = Ph, C6H4Me-4, C6H4NO2-4, C&tbd1;CPh) afford the products Cp2W2Ir3(μ4-η²-C2R)(μ-CO)(CO)9 [R = Ph (11), C6H4Me-4 (12), C6H4NO2-4 (13), C&tbd1;CPh (14)] in fair yields (23−45%). Product 12 has been structurally characterized, with the structural study revealing an edge-bridged tetrahedral metal core geometry and an unusual μ4-η² (3σ + π)-coordinated alkynyl ligand. The reaction corresponds to formal insertion of the alkynyltungsten reagent into an Ir−Ir linkage of 2. Reactions of 1 with these tungsten acetylides were not successful under the experimental conditions attempted, a result ascribed to steric constraints.