Cyclopentadienyl Analogues Research Articles

A 12-Vertex Metallacarborane of Silver(I).

The discovery of ferrocene in 1951 was a significant landmark in the field of organometallic chemistry, and since then, numerous sandwich- or half-sandwich metallic complexes have been reported. However, silver stands as an intriguing exception in this regard, and knowledge of its bonding situation has remained undisclosed. Herein, unprecedented 12-vertex metallacarboranes of Ag(I) (2a and 2b) were synthesized through the reaction of sodium hexamethyldisilazide (NaHMDS) with the mixture of nido-C2B9 carborane anion-supported N-heterocyclic carbene precursors (1a and 1b) and [Ag(PPh3)Cl]4. The X-ray structural analysis of the resulting metallacarboranes revealed a unique "slipped" half-sandwich structure, which is a rarity among cyclopentadienyl analogues. DFT calculations provided insights into the asymmetric π-interactions between the pentagonal C2B3 face and the silver ion.

On Neutral Unsaturated Ouroboric Borylenes.

The search is on for stable isolated borylenes. Potential roles in modern synthetic chemistry for boron analogues of carbenes continue to motivate interest in locating them. Using density functional and ab initio methods, we posit and examine the thermochemistry, and chemical bonding, including aromaticity, of several classes of 5- and 6-membered borylenic rings. In these systems, cyclization relies on dative bonding (ouroboric coordination) and π donation to a monovalent boron center from an adjacent O center. Certain neutral five-membered rings (heterocyclic cyclopentadienyl analogues) in particular are found to exhibit exceptionally strong preferences for the singlet multiplicity, each with singlet-triplet (S-T) gaps in excess of 40 kcal·mol-1. The singlet five-membered rings with the largest S-T gaps and some of the six-membered rings show evidence of weak aromaticity. Relationships of the form N = A·r-b, in line with Gordy's and other functions linking bond order, N, and covalent bond length, are identified for dative B←O contacts, r, reinforced in rings by π-delocalization.

Multimetallic Permethylpentalene Hydride Complexes.

The synthesis and characterization of group 4 permethylpentalene (Pn* = C8Me6) hydride complexes are explored; in all cases, multimetallic hydride clusters were obtained. Group 4 lithium metal hydride clusters were obtained when reacting the metal dihalides with hydride transfer reagents such as LiAlH4, and these species featured an unusual hexagonal bipyramidal structural motif. Only the zirconium analogue was found to undergo hydride exchange in the presence of deuterium. In contrast, a trimetallic titanium hydride cluster was isolated on reaction of the titanium dialkyl with hydrogen. This diamagnetic, mixed valence species was characterized in the solid state, as well as by solution electron paramagnetic resonance and nuclear magnetic resonance spectroscopy. The structure was further probed and corroborated by density functional theory calculations, which illustrated the formation of a metal-cluster bonding orbital responsible for the diamagnetism of the complex. These permethylpentalene hydride complexes have divergent structural motifs and reactivity in comparison with related classical cyclopentadienyl analogues.

The role of the phosphorus lone pair in the low-energy binuclear phospholyl vanadium carbonyl structures: comparison with cyclopentadienyl analogues

The structures and energetics of the binuclear phospholyl vanadium carbonyls (C4H4P)2V2(CO)n (n = 7, 6, 5, 4, 3, 2, 1) have been investigated using density functional theory. The lowest energy heptacarbonyl (C4H4P)2V2(CO)7 structures resemble those of the dimanganese pentacarbonyl (C4H4P)2Mn2(CO)5 with one seven-electron donor bridging η5,η1-C4H4P ring and no direct vanadium–vanadium bond. Similarly, the lowest energy hexacarbonyl (C4H4P)2V2(CO)6 structure resembles that of the dimanganese tetracarbonyl (C4H4P)2Mn2(CO)4 with two seven-electron donor bridging η5,η1-C4H4P rings and no direct vanadium–vanadium bond. The lowest energy pentacarbonyl (C4H4P)2V2(CO)5 structure has terminal η5-C4H4P phospholyl rings and a formal V≡V triple bond of length ~ 2.45 A similar to the experimentally known and structurally characterized cyclopentadienyl analogue (η5-C5H5)2V2(CO)5. Various combinations of V=V double bonds or V≡V triple bonds, four-electron donor bridging carbonyl groups and seven-electron donor bridging η5,η1-C4H4P rings are found in the more highly unsaturated derivatives (C4H4P)2V2(CO)n (n = 4, 3, 2) to give 17- and 18-electron vanadium configurations for triplet- and singlet-state structures, respectively. Formal V≣V quadruple bonds are found only in the highly unsaturated lowest energy singlet (C4H4P)2V2(CO)n (n = 2, 1) structures, which, however, lie at somewhat higher energies than isomeric triplet structures.

Comparison of binuclear phospholyl chromium carbonyl derivatives with their cyclopentadienyl analogues: Role of the phosphorus atom in ligand-metal bonding

The structures and energetics of the binuclear phospholyl chromium carbonyl derivatives (C4H4P)2Cr2(CO)n (n = 6, 5, 4, 3) have been investigated by density functional theory. The lowest energy (C4H4P)2Cr2(CO)n (n = 6, 4, 3) structures are completely analogous to their Cp2Cr2(CO)n analogues with two terminal pentahapto phospholyl rings. However, for the pentacarbonyl (C4H4P)2Cr2(CO)5 the lowest energy structure has a bridging seven-electron donor η5,η1-C4H4P ligand using the phosphorus lone pair in addition to the π-system of the phospholyl ligand as well as a Cr-Cr single bond. Thus, except for the pentacarbonyl the phosphorus lone pair of the phospholyl ligand is seen to play a minor role in the energetically preferred structures of the binuclear phospholyl chromium carbonyl derivatives.

(C4Me4)Co-containing triple-decker complexes with bridging heterocyclic ligands

(C4Me4)Co-containing triple-decker complexes with bridging boron and phosphorus heterocyclic ligands [(C4Me4)Co(μ-η:η-L)MCp*]+ (1: M = Fe, L = C5H5BMe; 2: M = Fe, L = C4Me4P; 3a: M = Fe, L = cyclo-P5; 3b: M = Ru, L = cyclo-P5) were synthesized by photochemical reaction of [(C4Me4)Co(C6H6)]+ with sandwich compounds Cp*ML. They were isolated as salts with PF6− anion, and the structures of 1PF6, 2PF6, and 3aPF6 were determined by X-ray diffraction. The μ-pentaphospholyl complex 3a was also synthesized by exchange of sandwich compounds in the μ-cyclopentadienyl triple-decker complexes [(μ-η:η-Cp){Co(C4Me4)}2]+ or [(C4Me4)Co(μ-η:η-Cp)FeCp]+. Complexes 1, 2, and 3a undergo nucleophilic degradation by acetone and acetonitrile with selective elimination of the [(C4Me4)Co]+ fragment giving the starting sandwich compounds. The rate of the nucleophilic degradation depends on the nature of the bridging ligand and decreases in the following order: C4Me4P ≥ C5H5BMe > cyclo-P5. The bonding in 1, 2, and 3a was analyzed and compared with that in the cyclopentadienyl analog [(C4Me4)Co(μ-η:η-Cp)FeCp*]+ using energy decomposition analysis.

Fe(C5Ar5)(CO)2Br] complexes as hydrogenase mimics for the catalytic hydrogen evolution reaction

A new iron-based hydrogenase mimic, [Fe(C5(p-C6H4Br)5)(CO)2Br], was synthesised and characterised using X-ray crystallography. Two analogous catalytic precursors, [Fe(C5Ar5)(CO)2Br] (Ar=C6H5; p-C6H4Br), were also analysed electrochemically in order to investigate how bulkier and more electron withdrawing C5Ar5 ligands affect the catalytic generation of hydrogen from trichloroacetic acid. Compared to previously reported iron-based cyclopentadienyl analogues, these complexes were found to have smaller overpotentials and larger turnover numbers. The [Fe(C5(p-C6H4Br)5)(CO)2Br] complex was found to be the most efficient of the two catalytic precursors with a turnover number of 25, an overpotential of around 310mV and a faster rate of reaction compared to [Fe(C5Ph5)(CO)2Br].

Indenylmetal Catalysis in Organic Synthesis.

Synthetic organic chemists have a long-standing appreciation for transition metal cyclopentadienyl complexes, of which many have been used as catalysts for organic transformations. Much less well known are the contributions of the benzo-fused relative of the cyclopentadienyl ligand, the indenyl ligand, whose unique properties have in many cases imparted differential reactivity in catalytic processes toward the synthesis of small molecules. In this Review, we present examples of indenylmetal complexes in catalysis and compare their reactivity to their cyclopentadienyl analogues, wherever possible.

Solid state structure of (pentamethylcyclopentadienyl)(2,4-dimethylpentadienyl)iron, Fe(C5Me5)(2,4-C7H11), and its incorporation into silica aerogels

The structure of Fe(C5Me5)(2,4-C7H11) has been determined (C7H11=dimethylpentadienyl), and found to be isomorphous with its ruthenium analogue. The Fe–C bond distances for the open pentadienyl ligand have been found to be about 0.02Å shorter than those for the aromatic pentamethylcyclopentadienyl ligand, whereas for the simple cyclopentadienyl analogue, the Fe–C bond distances for the two ligand types were nearly identical. While the structural data support proposals that the pentadienyl ligand is more strongly bound, the complex reacts readily with silica aerogel, during which it is the nonaromatic pentadienyl ligand which is removed via protonation. Solid state 13C NMR spectra are consistent with incorporation of the metal into one major environment, with lesser degrees of incorporation into alternative environments.

Dicationic μ‐Diborolyl Arene Triple‐Decker Complexes [CpCo(μ‐1,3‐C3B2Me5)M(arene)]2+ (M = Rh, Ir; Cp = Cyclopentadienyl): Synthesis, Structures, Electrochemistry and Bonding

AbstractThe reaction of the bromide complexes [CpCo(μ‐1,3‐C3B2Me5)MBr2]2 [M = Rh (1), Ir (2); Cp = cyclopentadienyl] with AgBF4 in acetonitrile affords the tris(acetonitrile) μ‐diborolyl triple‐decker complexes [CpCo(μ‐1,3‐C3B2Me5)M(MeCN)3]2+ [Rh (3), Ir (4)]. The labile nitromethane solvates [CpCo(μ‐1,3‐C3B2Me5)M(MeNO2)3]2+, generated in a similar way, react with benzene and its methylated derivatives to give the arene triple‐decker complexes [CpCo(μ‐1,3‐C3B2Me5)M(arene)]2+ [M = Rh (5), Ir (6); arene = C6H6 (a), 1,2,4,5‐Me4C6H2 (b), C6Me6 (c)]. The structures of 5b(BF4)2, 5c(BF4)2, 6b(BF4)2 and 6c(BF4)2 were determined by X‐ray diffraction. The electron‐transfer ability of the arene complexes was ascertained by electrochemical techniques. In general, they are able to undergo two separate one‐electron reductions reversibly. DFT calculations revealed structural changes caused by redox processes and satisfactorily predicted the redox potentials. The second reduction is accompanied by a η6 → η4 hapticity change of the arene ligand. Energy decomposition analysis revealed that the Rh–benzene bond in cation 5a is weaker than in cyclopentadienyl analogues [(C5R5)Rh(C6H6)]2+; however, 5a proved to be the least reactive in benzene replacement with acetonitrile and mesitylene.

Rotameric transformations in the photochemistry of TpM(CO)2(η(3)-C3H4R), where Tp = tris(pyrazolyl)borate, M = Mo or W, and R = H or Me.

Low energy photolysis of TpM(CO)2(η(3)-C3H4R), where Tp = tris(pyrazolyl)borate, M = Mo or W, and R = 2-H or 2-Me in PVC matrices at 85 K results in exo/gauche isomerism of the allyl ligand. This transformation comes in contrast to the behaviour observed in cyclopentadienyl analogues which undergo exo/endo isomerism. DFT computations reveal an η(3) → η(1)* → η(3) mechanism for the allyl rotameric interconversion where the η(1)*-allyl intermediate is generated upon MLCT excitation.

Triple-decker complex CpCo(μ-C3B2Me5)Rh(C2H4)2: Synthesis, structure and bonding

The reaction of the thallium derivative [CpCo(μ-C3B2Me5)]Tl with [Rh(C2H4)2Cl]2 affords the μ-diborolyl bis(ethylene) triple-decker complex CpCo(μ-C3B2Me5)Rh(C2H4)2 (4). Structure of 4 was determined by X-ray diffraction. According to DFT calculations, the ethylene dissociation energies for the triple-decker complexes CpCo(μ-C3B2R5)Rh(C2H4)2 (R=H, Me) are ca. 6kcalmol−1 lower than for cyclopentadienyl analogs (C5R5)Rh(C2H4)2. Energy decomposition analysis revealed that the bonding of anions [CpCo(C3B2R5)]− with [Rh(C2H4)2]+ is also weaker than that of [C5R5]−; the attractive interactions in both cases are 60–63% electrostatic and 37–40% covalent. The electrostatic potentials at the Rh nuclei suggest that the donor ability of the anions increases in the following order: Cp<[CpCo(C3B2H5)]⩽[CpCo(C3B2Me5)]<Cp∗.

Methylborabenzene ligands in binuclear iron carbonyl derivatives: High spin states and iron–iron multiple bonding

The experimentally known methylborabenzene iron carbonyl (C5H5BCH3)2Fe2(CO)4 and its decarbonylation products (C5H5BCH3)2Fe2(CO)n (n = 3, 2) have been studied by density functional theory for comparison with their cyclopentadienyl analogs. The lowest energy (η6-C5H5BCH3)2Fe2(CO)4 structures are the experimentally known singlet doubly bridged cis-(η6-C5H5BCH3)2Fe2(CO)2(μ-CO)2 and the corresponding trans isomer similar to the corresponding (η5-C5H5)2Fe2(CO)2(μ-CO)2 system. Also the triplet triply bridged (η6-C5H5BCH3)2Fe2(μ-CO)3 is the lowest energy tricarbonyl structure similar to the cyclopentadienyl system. However, significant differences between the methylborabenzene and cyclopentadienyl derivatives are found in the dicarbonyl systems. A singlet (η5-C5H5)2Fe2(μ-CO)2 structure with a short FeFe distance of ∼2.1 Å was previously found to be the lowest energy structure in the cyclopentadienyl system. An analogous methylborabenzene structure (η6-C5H5BCH3)2Fe2(μ-CO)2 is found as the lowest energy singlet structure. However, an unsymmetrical quintet (η6-C5H5BCH3)FeFe(CO)2(η6-C5H5BCH3) structure is predicted to lie ∼22 kcal/mol below this singlet structure. The existence of this low-energy, high-spin (η6-C5H5BCH3)2Fe2(CO)2 structure makes (η6-C5H5BCH3)2Fe2(μ-CO)3 disfavored with respect to disproportionation into (η6-C5H5BCH3)2Fe2(μ-CO)4 + (η6-C5H5BCH3)2Fe2(μ-CO)2 unlike its cyclopentadienyl analog.

Synthesis and Characterization of Free and Coordinated 1,2,3-Tripnictolide Anions

We have investigated the chemical reactivity of heptaatomic anionic clusters of the group 15 elements ([E7]3–/[HE7]2–, E = P, As) toward the symmetric and asymmetrically substituted alkynes diphenylacetylene and phenylacetylene. The results reported herein, alongside a previous report on the reactivity of such clusters toward acetylene, describe a versatile route by which to access otherwise elusive 1,2,3-tripnictolide anions of the general formula [E3C2RR′]− (R = R′ = H, E = P (1), As (2); R = R′ = C6H5, E = P (3) As (4); R = H, R′ = C6H5, E = P (5), As (6)). These species can be isolated as [K(18-crown-6)]+ or [K(2,2,2-crypt)]+ salts. All anions were characterized by multielement NMR spectroscopy and electrospray mass spectrometry. In addition, single-crystal X-ray diffraction structures of the novel species [K(18-crown-6)(THF)2][3], [K(2,2,2-crypt)][4]·xTHF (x = 0, 0.5), and [K(18-crown-6)THF][6] were also obtained. The chemical reactivity of these group 15 cyclopentadienyl analogues has been explored ...

Highly selective ethylene trimerization catalyzed by half-sandwich indenyl titanium complexes with pendant arene groups and MAO

A series of half-sandwich indenyl titanium complexes [Ind-(bridge)-Ar]TiCl3 (C1–C9) bearing pendant arene group on indenyl ring have been synthesized and used for the catalytic ethylene trimerization to 1-hexene in the presence of MAO. The molecular structures of complexes C3 [Ind-C(cyclo-C5H10)-Ph]TiCl3 and C5 [Ind-C(cyclo-C5H10)-(p-MePh)]TiCl3 have been established by single-crystal X-ray diffraction study. No intramolecular coordination interaction between the arene moiety and the titanium center could be observed in the solid state of these complexes. At 0°C and 0.8MPa of ethylene pressure, upon activation with MAO, C3 possesses the highest activity of 1968kg of 1-hexene/(mol-Tih) and the overall selectivity of 95.9% by mass for 1-hexene, and is also more active than the corresponding cyclopentadienyl analog [Cp-C(cyclo-C5H10)-Ph]TiCl3 (C10) under the identical conditions. The substituents of various steric and electronic effects on the pendant arene group and the bridge unit between the indenyl and this arene group exert great influence on the activity and selectivity of these indenyl titanium complexes for ethylene trimerization to 1-hexene. Similar to cyclopentadienyl analogs, upon activation with MAO the resultant indenyl catalytic systems also show great sensitivity to the temperature. With the increase of the reaction temperature, both the activity and selectivity of 1-hexene declined.

Nine-Electron Donor Bridging Indenyl Ligands in Binuclear Iron Carbonyls

The recent (2011) discovery of two nine-electron donor bridging indenyl ligands in the cobalt sandwich complex {η5,η4-Me3Si)2C9H5}2Co2 makes of interest a search for structures of metal carbonyl derivatives with such indenyl ligands. In this connection, density functional theory studies on the binuclear iron carbonyls (C9H7)2Fe2(CO)n (n = 4, 3) predict structures having terminal pentahapto indenyl ligands similar to the experimentally known structures for their cyclopentadienyl analogues (C5H5)2Fe2(CO)n. Thus, the lowest-energy (C9H7)2Fe2(CO)4 structures are singlets with two bridging CO groups. Similarly, the lowest-energy (C9H7)2Fe2(CO)3 structures are triplets with three bridging CO groups and terminal pentahapto indenyl ligands. However, a nine-electron donor bridging indenyl ligand is found in the lowest-energy (C9H7)2Fe2(CO)2 structure, which has an Fe–Fe single bond and two terminal CO groups. Higher-energy (C9H7)2Fe2(CO)2 structures with terminal pentahapto indenyl ligands and short (∼2.1 A) Fe≡Fe...

Half‐Titanocence Anilide Complexes Cp′TiCl2[N(2,6‐R12C6H3)R2]: Synthesis, Structures and Catalytic Properties for Ethylene Polymerization and Copolymerization with 1‐Hexene

AbstractA number of new half‐sandwich titanium(IV) complexes of the type [Cp′TiCl2{N(2,6‐R12C6H3)R2}] [R1 = iPr (1, 2, 4), Me (3, 5); R2 = Me (1, 3, 4, 5), Bn (2); Cp′ = Cp (1, 2, 3), Cp* (4, 5)] have been synthesized by the reaction of [Cp′TiCl3] with the lithium salts of the corresponding anilide in toluene or diethyl ether. All titanium complexes were characterized by 1H and 13C NMR spectroscopy and elemental analyses. The molecular structures of complexes 1, 4, and 5 were determined by single‐crystal X‐ray diffraction analysis. When activated with AliBu3 and Ph3CB(C6F5)4, complexes 1–5 exhibited reasonable catalytic activity in ethylene polymerization, producing high‐ or ultra‐high‐molecular‐weight polyethylene. It was found that complex 4 shows the highest catalytic activity in ethylene polymerization and complexes 1–3 produced ultra‐high‐molecular‐weight (Mη &gt; 3 × 106 g mol–1, viscosity‐average molecular weight) polyethylene. The copolymerization of ethylene with 1‐hexene catalyzed by these complexes in the presence of AliBu3/Ph3CB(C6F5)4 was also investigated. Complexes 4 and 5 with the pentamethylcyclopentadienyl ligand were found to show higher catalytic activity in ethylene/1‐hexene copolymerization and produced poly(ethylene‐co‐1‐hexene)s with much higher molecular weights and co‐monomer incorporation than their cyclopentadienyl analogues 1–3 under similar conditions. The co‐monomer incorporation abilities of complexes 4 and 5 are relatively high in comparison with other half‐sandwich titanium catalyst systems.

More electron rich than cyclopentadienyl: 1,2-diaza-3,5-diborolyl as a ligand in ferrocene and ruthenocene analogs

Ruthenium and iron sandwich complexes incorporating cyclopentadienyl analogs with CB(2)N(2)(-) skeletons were characterized. Electrochemical measurements supported by computational studies revealed that in combination with larger metal ions such as Ru the CB(2)N(2)(-) ligand can be more electron-rich than its organic counterpart.

Chromium–Chromium Bonding in Binuclear Azulene Chromium Carbonyl Complexes

The experimentally known cis-[(η 5 ,η 5 -C 10 H 8 )Cr 2 (CO) 6 ] structure with a rather long formal Cr―Cr single bond of about 3.3 A is predicted by density functional theory to be the lowest energy C 10 H 8 Cr 2 (CO) 6 structure. However, a trans-[(η 7 ,η 5 -C 10 H 8 )Cr 2 (CO) 6 ] structure lies in energy within ca. 4 kcal/mol of this global minimum. The lowest energy structures for the unsaturated derivatives C 10 H 8 Cr 2 (CO) n (n = 5, 4, 3, 2) are all related structures with cis stereochemistry of the two chromium atoms, a chromium-chromium bond, and a single bridging carbonyl group. Such structures include singlet cis-[(η 5 ,η 5 -C 10 H 8 )Cr 2 (CO) 4 (μ-CO)], singlet cis-[(η 7 ,η 5 -C 10 H 8 )Cr 2 (CO) 3 (μ-CO)], triplet cis-[(η 7 ,η 5 -C 10 H 8 )Cr 2 -(CO) 2 (μ-CO)], and triplet cis-[(η 7 ,η 5 -C 10 H 8 )Cr 2 (CO)(η 2 -μ-CO)], for n = 5, 4, 3, and 2, respectively. The C 10 H 8 Cr 2 (CO) 5 structure is thermodynamically viable with respect to disproportionation into C 10 H 8 Cr 2 (CO) 6 and C 10 H 8 Cr 2 (CO) 4 , in contrast to its cyclopentadienyl analogue [(η 5 -C 5 H 5 ) 2 Cr 2 (CO) 5 ]. However, the C 10 H 8 Cr 2 (CO) 4 structure is thermodynamically unfavorable with respect to disproportionation into C 10 H 8 Cr 2 (CO) 5 and C 10 H 8 Cr 2 (CO) 3, in contrast to its very stable and experimentally known cyclopentadienyl analogue [(η 5 -C 5 H 5 ) 2 Cr 2 (CO) 4 ]. The lowest energy structure cis-[(η 7 ,η 5 -C 10 H 8 )Cr 2 (μ-CO)] for the monocarbonyl C 10 H 8 Cr 2 (CO) is a triplet structure with an unsymmetrical bridging carbonyl group and a Cr=Cr distance of about 2.4 A, suggesting a formal triple bond. The qualitatively assigned Cr―Cr formal bond orders (one through five) are remarkably consistent with the Wiberg bond indices obtained from the Weinhold natural bond order analysis.

ChemInform Abstract: Organo-Transition Metal Compounds Containing Perfluorinated Ligands

Publisher Summary This chapter discusses the effect of α-fluorine substituents on the structure and reactivity of organic ligands bound to transition-metal centers, with particular emphasis on recent chemistry of octafluorocycloocta-1,3,5,7-tetraene (OFCOT). The chemistry of transition-metal compounds containing hydrocarbon ligands continues to be intensively explored. The most common kinds of compounds are those with metal–carbon σ bonds and metal–olefin bonds. The physical properties and chemical reactivity of transition-metal compounds containing trifluoromethyl ligands are surveyed. Complexes of cyclic perfluoroolefins are also quite common. In contrast to their hydrocarbon analogues, many unsaturated fluorocarbons react with anionic transition-metal nucleophiles to yield products arising from the net displacement of fluoride ion. The fluorocarbon complexes are notably different in their chemical properties as compared to their hydrocarbon analogues. The regio- and stereochemistry of phosphine attack were unambiguously defined by a single-crystal X-ray diffraction study. The enhanced reactivity of the indenyl complexes of the transition metals toward ligand substitution, compared to their cyclopentadienyl analogues, is due to a slippage of the indenyl ligand from η5 to an η3 bonding mode, thus making the metal center coordinatively unsaturated. Further contrasting reactivity is observed using t-butylisocyanide (t-BuNC) as the exogenous ligand. No photochemical rearrangements or transannular ring closure chemistry were observed with the corresponding cyclopentadienyl analogues. Additional chromatography allowed for the isolation of minor amounts of a second isomeric complex that could not be totally separated from the major isomer.