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As complex materials are widely used in emerging technologies for environmental and energy applications, it is important to be able to quantify their stimuli-response behaviors. Light is a useful stimulus to modulate multifunctional electrochemical, magnetic, optical, and structural properties in metal–organic frameworks (MOFs); however, the underlying mechanisms and kinetics of light-induced structural changes are not well understood. Herein, a double [2 + 2] photocyclization in photoactive [Cd2(stil)2(Py2TTF)2] (stil2– = 4,4′-stilbenedicarboxylic acid, Py2TTF = 2,6-bis(4′-pyridyl)-tetrathiafulvalene) offers a powerful platform to quantitatively probe solid-state photocyclization kinetics. Variable-temperature Raman spectroscopy revealed a nonlinear temperature dependence of these parameters, which could be analyzed using the Johnson–Mehl–Avrami–Kolmogorov (JMAK) kinetic model to yield a maximum rate observed between 0 °C and 20 °C of approximately 0.172 s–1. These results offer the first example of the quantification of the photocyclization kinetics in a MOF. Density functional theory (DFT) calculations support a singlet reaction mechanism for the double [2 + 2] photocyclization, which is facilitated by the cofacial alignment of Py2TTF ligands. Establishing mechanistic and kinetic models that can be applied to multistimuli-responsive materials provides a powerful platform for their future design for applications in sensing, switching, and molecular separations.

A detailed study of the two-dimensional (2-D) Hofmann-like framework [Fe(furpy)

Binding hydrophilic anions such as sulfate in water is a significant academic challenge, in particular for neutral receptors. To achieve this, typically a large molecular receptor is designed that wraps around a bound anion in a hydrophobic microenvironment. Such receptors require multi-step synthesis and often display selectivity towards hydrophobic anions such as iodide. We here report the one-pot synthesis of a [2.2.2]urea cryptand (cage) and its ability to bind sulfate in water with sub-millimolar affinity achievable by incorporation into micelles. Unlike existing neutral receptors, the cage has >10-fold selectivity for sulfate against hydrophobic anions even in pure water. The cage displays rare slow-exchange NMR responses to divalent anions in DMSO-water allowing for simultaneous analysis of multiple divalent anions in water analogous to an ion chromatography instrument. Our results demonstrate the pre-organization of strong directional NH hydrogen bond donors in a cage scaffold as a synthetically less-demanding, yet effective approach to achieving selective binding of hydrophilic anions in water.

The achievement of targeted properties in spin crossover (SCO) materials is complicated by often unpredictable cooperative interactions in the solid state. Herein, we report a dinuclear Fe(II) triple helicate 1, which is a rare example of a SCO material possessing two distinct magnetic behaviors that depend upon the thermal scan rate. Desolvated 1 was seen to undergo spin transition (ST) which was complete following slow cooling (1 K min-1), but incomplete ST (corresponding to 50% conversion) on fast cooling (10 K min-1). The incomplete ST observed in the latter case was accompanied by a higher temperature onset of ST, differing from TIESST (Temperature-Induced Excited Spin-State Trapping) materials. The two SCO pathways have been shown to arise from the interconversion between two structural phases (a and b), with both phases having associated high spin (HS) and low spin (LS) states. SCXRD (Single Crystal X-ray Diffraction) experiments using controlled cooling rates and a synchrotron light source enabled short collection times (2-3 minutes per dataset) which has enabled the identification of a mechanism by which the slow-cooled material may fully relax. In contrast, fast-cooled materials exhibit disordered arrangements of multiple structural phases, which has in turn revealed that the [HS-LS] ↔ [LS-HS] equilibria are controllable in the solid by varying the scan rate. Such behavior has been previously observed in solution studies, but its control in solids has not been reported up to now. This study demonstrates how intermolecular cooperativity can allow multiple distinct magnetic behaviors, and provides some insight into how [HS-LS] ↔ [LS-HS] equilibria can be controlled in the solid state, which may assist in the design of next-generation logic and signaling devices.

A range of morphologically distinct metallosupramolecular Cu(II) and Pd(II) complexes has been constructed, based on the tritopic ligand 1,1',1″-(benzene-1,3,5-triyl)tris(4,4-dimethylpentane-1,3-dione) (H). By control of the reaction conditions, it is possible to generate distinct coordination assemblies possessing either macrocyclic or polymeric structures and more importantly distinct activity in catalysis of the Suzuki-Miyaura cross-coupling.

A spin-crossover (SCO) active dinuclear Fe(II) triple helicate of the form [Fe] was combined with additional supramolecular components in order to manipulate the interhelical separation and steric congestion and to study the magneto-structural effects on the ensuing composite materials. A more separated array of SCO units produced more extensive spin-transitions, while a tightly arranged lattice environment stabilized the low-spin state. This study highlights the important interplay between crystal packing, intermolecualr interactions, and the magentic behavior of SCO materials.

We probe, here, a family of 2D Hofmann-type frameworks, [FeII(Pd(CN)4)(bztrzX)2]·nH2O [X·nH2O; X = F, Cl, Br; n = 1 (X = Cl, Br) and 3 (X = F); bztrzX = (E)-1-(2-Xphen-1-yl)-N-(4H-1,2,4-triazol-4-yl)methanimine], with halogen-appended ligands. In all cases, there are two crystallographically distinct FeII sites, ({Fe1-Fe2}), driven by the presence of a range of host-host and host-guest interactions. We find that lattice modification through X variation influences the elastic coupling between the FeII sites, the emergence of ferroelastic or antiferroelastic interactions between these sites, and the relative spin-state stabilization/destabilization at each site. In Cl·H2O, the FeII sites show strong elastic coupling, as evidenced by both FeII sites undergoing a spin transition in a single cooperative step, as driven by the volume strain over the high-spin (HS)-to-low-spin (LS) transition. The FeII sites in F·3H2O are also elastically coupled; however, the change of the X atom characteristics and increased guest molecules in the pores result in an antiferroelastic interaction characteristic between Fe1 and Fe2 and a resultant two-step spin-state transition. The change of the X atom to Br in Br·H2O results in the FeII sites being decoupled due to halogen atom steric bulk, resulting in the independent spin-state transition of Fe1 and Fe2 sites and a two-step spin-state transition pathway. Uniquely, all three possible spin-state transition pathways of a two-site switching system are observed in this family [(1) {HS-HS} ↔ {HS-LS} ↔ {LS-LS} for Br·H2O, (2) {HS-HS} ↔ {LS-HS} ↔ {LS-LS} for F·3H2O, and (3) {HS-HS} ↔ {LS-LS} for Cl·H2O for {Fe1-Fe2}]. Overall, these findings broadly support recent theoretical models but highlight that additional structural and topological complexities are needed to form a holistic picture of the drivers of elastic frustration.

Molecular machines and switches, supramolecular chemistry, and crystal engineering are vibrant areas of research. Organic chemists have devoted considerable efforts to develop a wide range of complex functional building blocks with enhanced properties and chemically responsive properties to advance these fields. However, the rational design of topologically versatile and chemically responsive building blocks in the main group arena is largely unexplored. Within this context, we have rationally designed a series of NH-bridged acyclic dimeric cyclodiphosphazanes species, [(μ-NH){PE(μ-NtBu)2PE(NHtBu)}2] (E= O and S), displaying bimodal bifurcated R21(8) and trifurcated R31(8,8) hydrogen bonding motifs. The reported species reversibly switch their topological arrangement in the presence of anions. Our results underscore these species as versatile building blocks for molecular machines and switches, as well as supramolecular chemistry and crystal engineering based on cyclophosphazane frameworks.

Preferential formation of cis- or trans-palladium(II) complexes controlled via the exocyclic binding sites embedded in dithiamacrocycles (L1 = -S(CH2)2S-; L2 = -S(CH2)2O(CH2)2S-) is reported. From the reaction with K2PdCl4, the shorter sulfur-to-sulfur separation in L1 preferentially leads to the formation of cis-[Pd(L1)Cl2] (1), while L2, incorporating a larger sulfur-to-sulfur separation, coordinates in a trans fashion to form a cyclic dimer, trans-[Pd2(L2)2Cl4] (2). The observed results illustrate the possibility for the controlled formation of cis/trans square-planar complexes through binding-site design. When palladium(II) acetate was substituted for K2PdCl4 in the above reaction, L1 gave no product, while L2 resulted in the formation of a unique tripalladium(II) complex, [Pd3(L2)(CH3C(═N)OC(═N)CH3)(CH3COO)4] (3), in which three PdII atoms are linked by acetimidic anhydride, CH3C(═N)OC(═N)CH3, derived from the acetonitrile solvent employed. In the 1H NMR spectrum for 3, specific methylene signals for methylene protons adjacent to S donors exhibit large complexation-induced splitting of the geminal proton signals into axial and equatorial proton peaks, thus indicating magnetically nonequivalent geminal protons that reflect the restricted conformation of the metallabicycle.

A two-dimensional molecular square (MC) was obtained by the self-assembly of a bis(tetrazole) linker, 4,4'-bis(1H-tetrazol-5-yl)-1,1'-biphenyl (H2L1), with a square-planar metal acceptor M [M = (tmeda)Pd(NO3)2, where tmeda = N,N,N',N'-tetramethylethane-1,2-diamine] in dimethyl sulfoxide (DMSO) followed by crystallization. The uncommon 2,3-binding mode through N atoms of the tetrazole rings in this assembly leads to the formation of an octanuclear molecular square. The molecular square MC [Pd8(L1)4(NO3)8] is unstable in DMSO and slowly converts to a dynamic mixture of a 3D tetrahedral cage T1 [Pd12(L1)6(NO3)12] and the macrocycle MC. A tetrahedral cage (T1) is formed by the usual 1,3-binding mode of the tetrazole rings. However, self-assembly of the T1 [Pd12(L1)6(PF6)12] was possible to access in the pure form in a less polar solvent like acetonitrile. The pure T1 [Pd12(L1)6(PF6)12] also converts to a mixture of T1 and MC in DMSO. Interestingly, when a tris(tetrazole) linker, tris(4-(1H-tetrazol-5-yl)phenyl)amine (H3L2), was treated with the acceptor M, it produced a tetrahedral nanocage T2 [Pd12(L2)4(NO3)12] through 1,3-binding mode of the tetrazole rings without any trace of an octahedral cage through 2,3-binding mode of the tetrazole moieties.

The structural changes that occur in the strongly hysteretic spin-crossover complex [Fe(qsal-I)2]NTf2 (1) have been determined for the full width of the hysteresis. In the cooling mode, structural ...

Encasing the classic spin-crossover (SCO) complex cation [Co(terpy)2]2+ in different anionic supramolecular frameworks modulates its SCO behavior, tuning both its T1/2 (shift of up to 200 K) and th...

Two new oxygenated terpenes (1 and 2) have been characterized from the Australian nudibranch Goniobranchus coi. Broadened 1H NMR signals, together with the absence of individual carbon NMR signals, complicated analysis of 5,9-epoxydendrillolide A (1); increasing the temperature to 323 K revealed the missing NMR signals. Low-temperature 1H NMR experiments provided an activation barrier of ∼15 kcal mol–1 and, together with DFT calculations, supported interconversion of a twist chair conformer with two different chair conformers. X-ray crystallographic analysis coupled with biosynthetic reasoning suggested a (5R, 8S, 9R, 13R, 14R, 15R, 16R) configuration. Ketone 2 demonstrated similar dynamic conformational processes to 1.

The encapsulation of metal complexes within halogen-bonded networks may lead to modulation of their properties in the solid state without the need to chemically incorporate donor or acceptor moieties on the metal complex itself. Here, we investigate the effect of anionic halogen-bonded structure formation on the organization of arene-rich bis(4′-phenyl-2,2′:6′,2″-terpyridine)nickel(II) cations, varying both the topicity and the geometry of the halogen bond donor in a heteromeric three-component system. The X-ray structures of four cocrystals (1-4), [Ni(terpy-ph)][(1,2-DITFB)(I)] (1), [Ni(terpy-ph)][(1,3-DITFB)(I)] (2), [Ni(terpy-ph)][(1,4 DITFB)(I)](I)·9HO (3), and [Ni(terpy-ph)][(1,3,5-TITFB)(HO)(I)]·2HO (4), as well as the iodide salt of the parent complex [Ni(terpy-ph)]I·4HO are reported along with characterization to assess bulk sample and phase purity. Within assemblies of complex cations, we observe the ubiquitous aryl embrace motif often seen in the crystal packing of such terpyridine complexes; however, these assemblies are separated from one another by a variety of halogen-bonded structures, including discrete supramolecular complexes, 1D chains, pseudo-2D sheets, and unusual racemic double helices. The results herein demonstrate how typical crystal packing motifs of metal terpy-ph complexes can be altered and disrupted through their incorporation into halogen-bonded heteromeric three-component systems.

Herein, we report an unprecedented combination of pre-arranged building blocks and a multi-step synthetic route to rationally and simultaneously enable access to an unfolded tetrameric macrocycle, which is not accessible using conventional synthetic strategies. The obtained macrocycle, cis-[μ-P(μ-NtBu)]2(μ-p-OC6H4C(O)O)]4[μ-P(μ-NtBu)]2 (4), is the first unfolded open-face hybrid cyclodiphosphazane macrocycle reported and displays a cavity area of 110.1 Å2 - the largest of its kind.

The ability to tune physical properties is attractive for the development of new materials for myriad applications. Understanding and controlling the structural dynamics in complicated network structures like coordination polymers (CPs) is particularly challenging. We report a series of two-dimensional CPs [Mn(salen)]2[M(CN)4]·xH2O (M = Pt (1), PtI2 (2), and MnN (3)) incorporating zigzag cyano-network layers that display composition-dependent anisotropic thermal expansion properties. Variable-temperature single-crystal X-ray structural analyses demonstrated that the thermal expansion behavior is caused by double structural distortions involving [Mn(salen)]+ units incorporated into the zigzag layers. Thermal relaxations produce structural transformations resulting in positive thermal expansion for 2·H2O and negative thermal expansion for 3. In the case of 1·H2O, the relaxation does not occur and zero thermal expansion results in the plane between 200 to 380 K. The present study proposes a new strategy base...

Zero in-plane thermal expansion (TE) in a two-dimensional (2D) coordination polymer is demonstrated. The combination of components that expand and those that shrink into zigzag layers results in no net area change in the 2D materials with temperature. Single crystals of [Mn(salen)]2[Mn(N)(CN)4(guest)] (salen = N,N′-ethylenebis(salicylideneaminato), guest = MeOH and MeCN) were prepared, and variable-temperature single-crystal X-ray structural analyses demonstrated that these compounds exhibited both anisotropic positive and negative thermal expansion depending on the guest species. The TE behavior results from distortions of the octahedral coordination geometry of [Mn(salen)]+ units in the zigzag layers. When both guests MeOH and MeCN were incorporated into one material, [Mn(salen)]2[Mn(N)(CN)4(MeOH)0.25(MeCN)0.75], zero in-plane TE resulted in a range of temperature between 380 and 440 K.

The combination of the dicopper platform [Cu2(L)2(THF)2] (1·2THF), where H2L is 1,1'-(1,3-phenylene)-bis-4,4-dimethylpentane-1,3-dione, and 1,4-bis(4-pyridyl)piperazine (bpp), afforded the first example of a one-dimensional polyrotaxane {[(1)(μ2-bpp)][(1)2(bpp)2]}n whose "string" and "bead" are constructed from the same components. The bead of stoichiometry [(1)2(bpp)2] has a large rectangular cavity of dimensions 7.40 × 15.64 Å and is threaded onto a stair-like string of composition [(1)(μ2-bpp)]n. The formation of the polyrotaxane is driven by π-π stacking between the string and the beads with precise electronic and steric complementarity between these components. A pathway for the formation of the polyrotaxane is proposed.

Different anionic templates act to give rise to four distinct Cd(II)-based architectures: a Cd2L3 helicate, a Cd8L12 distorted cuboid, a Cd10L15 pentagonal prism, and a Cd12L18 hexagonal prism, which respond to both anionic and cationic components. Interconversions between architectures are driven by the addition of anions that bind more strongly within a given product framework. The addition of Fe(II) prompted metal exchange and transformation to a Fe4L6 tetrahedron or a Fe10L15 pentagonal prism, depending on the anionic templates present. The equilibrium between the Cd12L18 prism and the Cd2L3 triple helicate displayed concentration dependence, with higher concentrations favoring the prism. The Cd12L18 structure serves as an intermediate en route to a hexafluoroarsenate-templated Cd10L15 complex, whereby the structural features of the hexagonal prism preorganize the system to form the structurally related pentagonal prism. In addition to the interconversion pathways investigated, we also report the single-crystal X-ray structure of bifluoride encapsulated within a Cd10L15 complex and report solution state data for J-coupling through a CH···F(-) hydrogen bond indicating the strength of these interactions in solution.

Differential binding affinities for a set of anions were observed between larger (1) and smaller (2) tetrahedral metal-organic capsules in solution. A chemical network could thus be designed wherein the addition of hexafluorophosphate could cause perchlorate to shift from capsule 2 to capsule 1 and triflimide to be ejected from capsule 1 into solution.

A rigid organic ligand, formed through the subcomponent self-assembly of p-toluidine and 6,6'-diformyl-3,3'-bipyridine, was employed in a systematic investigation into the synergistic and competing effects of metal and anion templation. A range of discrete and polymeric metal-organic complexes were formed, many of which represent structure types that have not previously been observed and whose formation would not be predicted on taking into account solely geometric considerations. These complex structures, capable of binding multiple guests within individual binding pockets, were characterized by NMR, ESI-MS, and single-crystal X-ray diffraction. The factors that stabilize individual complexes and lead to the formation of one over another are discussed.

A general method for preparing Fe(4)L(4) face-capped tetrahedral cages through subcomponent self-assembly was developed and has been demonstrated using four different C(3)-symmetric triamines, 2-formylpyridine, and iron(II). Three of the triamines were shown also to form Fe(2)L(3) helicates when the appropriate stoichiometry of subcomponents was used. Two of the cages were observed to have nearly identical Fe-Fe distances in the solid state, which enabled their ligands to be coincorporated into a collection of mixed cages. Only one of the cages combined a sufficiently large cavity with the sufficiently small pores required for guest binding, taking up a wide variety of guest species in size- and shape-selective fashion.

Five new silver(I) coordination polymers of types [Ag2L1(NO3)2]n (1), [Ag2L2(NO3)2]n (2), [Ag2L3(NO3)2]n (3), [Ag2L4(NO3)2]n (4), and [AgL5(NO3)]n (5) have been synthesized, where L1–L5 are the Schiff base ligands formed from 2:1 condensation of acetylacetone with the symmetrical diamines H2N(CH2)nNH2, with n = 2 and 6 to give L1 and L2, 1,2-bis(2-aminophenoxy)ethane to give L3, 1,4-bis(2-aminophenoxy)butane to give L4, and 1,6-bis(4-aminophenoxy)butane to give L5. The single crystal X-ray structures of the Ag(I) complexes 1–5 have been determined. Both 1 and 2 adopt three-dimensional polymeric network structures, while 3–5 adopt two-dimensional-layered framework structures. In 1 and 2, the terminal O and γ-C atoms of two acacH-imine domains of the same ligand bind to different silver ions, while in each of 3–5 a γ-C from one or both acacH-imine domains binds to a silver ion, with the remaining coordination sites occupied by bridging monodentate or bidentate nitrato groups and/or a Schiff base ligand oxyg...

The interaction of Cu(II) with three β-diketone ligands of type R1C(O)CH2C(O)R2 (where R1 = 2-, 3-, or 4-pyridyl and R2 = C6H5, respectively), HL1−HL3, along with the X-ray structures and the pKa values of each ligand, are reported. HL1 yields a dimeric complex of type [Cu(L1)2]2. In this structure, two deprotonated HL1 ligands coordinate in a trans planar fashion around each Cu(II) center, one oxygen from each CuL2 unit bridges to an axial site of the second complex unit such that both Cu(II) centers attain equivalent five-coordinate square pyramidal geometries. The two-substituted pyridyl groups in this complex do not coordinate, perhaps reflecting steric factors associated with the closeness of the pyridyl nitrogen to the attached (conjugated) β-diketonato backbone of each ligand. The remaining two Cu(II) species, derived from HL2 and HL3, are both coordination polymers of type [Cu(L)2]n in which the terminal pyridine group of each ligand is intermolecularly linked to an adjacent copper center to gener...

The metal complexation properties of the naturally occurring Maillard reaction product isomaltol HL(2) are investigated by measurement of its stability constants with copper(II), zinc(II), and iron(III) using potentiometric pH titrations in water, by structural and magnetic characterization of its crystalline complex, [Cu(L(2))(2)]·8H(2)O, and by density functional theory calculations. Strong complexation is observed to form the bis(isomaltolato)copper(II) complex incorporating copper in a typical (pseudo-)square-planar geometry. In the solid state, extensive intra- and intermolecular hydrogen bonding involving all three oxygen functions per ligand assembles the complexes into ribbons that interact to form two-dimensional arrays; further hydrogen bonds and π interactions between the furan moiety of the anionic ligands and adjacent copper(II) centers connect the complexes in the third dimension, leading to a compact polymeric three-dimensional (3D) arrangement. The latter interactions involving copper(II), which represent an underappreciated aspect of copper(II) chemistry, are compared to similar interactions present in other copper(II) 3D structures showing interactions with benzene molecules; the results indicate that dispersion forces dominate in the π system to chelated copper(II) ion interactions.

A rare, discrete, mixed-valent, heterometallic Fe(III)/Cu(II) cage, [Cu6Fe8L8](ClO4)12·χsolvent (H3L = tris{[2-{(imidazole-4-yl)methylidene}amino]ethyl}amine), was designed and synthesized via metal-ion-directed self-assembly with neutral tripodal metalloligands. The formation of this coordination cage was demonstrated by X-ray crystallography, ESI mass spectrometry, FT-IR, and UV-vis-NIR spectroscopy.

The formation of 3D fused 10-membered “bracelet” frameworks derived from the alkyl-substituted curcurbit[5]urils (SQ[5]s), 1,2,4-hexamethylcucurbit[5]uril (1,2,4-HMeQ[5]), and pentacyclopentanocucurbit[5]uril (PCyHQ[5]) and K+ ions is described. These remarkable catenated structures feature trigonal-planar branching units involving three SQ[5]s connected via their bound K+ ions in a triangular manner in which the coordination of each K+ ion to the five portal carbonyl oxygen atoms of one SQ[5] as well as to a bridging portal carbonyl oxygen from an adjacent SQ[5] draws the edges of three portals into close proximity. The corresponding offset angle at each junction provides the basis for the 3D assembly of the observed fused 10-membered SQ[5] bracelet frameworks.

Cyclic tetrapeptides have generated great interest because of their broad-ranging biological properties. In order to synthesize these highly strained 12-membered cyclic compounds, a cyclization strategy using pseudoprolines as removable turn inducers has been developed. The pseudoproline derivatives induce a cisoid amide bond in the linear peptide backbone which facilitates cyclization. After cyclization, the turn inducers can be readily removed to afford cyclic tetrapeptides containing serine or threonine residues.

The synthesis of two new bifuctional ligand sytems incorporating two different “classical” coordination units connected by a bent (but flexible) thioether linkage is reported. The new systems are the β-diketone-pyridyl derivative, 3-(pyridin-4-ylthio)pentane-2,4-dione (L1), and its hydrazine condensation product, the pyridyl-pyrazole species 4-(3,5-dimethyl-1H-pyrazol-4-ylthio)pyridine (L2). Both systems were designed for use in metal−organic framework studies. With L1, four metal-containing products were crystallized, [Cu(L1−H)2]n (1), {[Cu(L1−H)2]·0.5H2O·CHCl3}n (2), {[Zn(L1−H)2]·2H2O}n (3), and [Zn(L1−H)2]·2MeOH}n (4); these display three different array types. Compound 1 incorporates 5-coordinate Cu(II) ions with square pyramidal stereochemistry. The β-diketonato groups from two ligands coordinate in the basal plane with the apical position occupied by a pyridyl nitrogen from a third ligand that bridges to an adjacent copper center. Propagation of this coordination motif produces a 1D chain. In 2, whi...

A series of novel indolyl-imine ligand precursors have been synthesized. In particular, bidentate, tridentate, and potentially tetradentate ligands were prepared, each containing both indolyl sp2-N and imine sp2-N donors. A series of neutral rhodium(I) and iridium(I) complexes of these ligands were synthesized, including monometallic and bimetallic complexes. The X-ray structures of three of the monometallic complexes with bidentate indolyl-imine ligands were determined. In each complex, the metal center was in a square planar conformation, as expected for Rh(I) and Ir(I) complexes. The fiveand six-membered metallocycles formed on complexation of the metal with the ligands were all planar, and the aromaticity of the ligands was maintained. The Rh(I) complex with the tridentate indolyl ligand (L) reacted at room temperature with CH2Cl2 to form the Rh(III) chloromethyl complex [Rh(L)(CO)-(CH2Cl)(Cl)] via oxidative addition of the C-Cl bond of CH2Cl2. The Rh/Ir(I) indolyl-imine complexes are efficient catalysts for the intramolecular cyclization of 4-pentynoic acid to form c-methylene-c-butyrolactone. A dinuclear Rh(I) complex was the most active catalyst, demonstrating a significant degree of bimetallic cooperativity.