Half-sandwich Cp*Ir and Cp*Rh metalacycles have been successfully applied in traditional domains encompassing organic transformations and catalysis in recent years, especially the catalytic activation of C-H bonds. Cyclometalation has proven to be a highly attractive and versatile synthetic method for the formation of organometallic metalacycles. This review intends to describe isolated and well-defined cyclometalated iridium/rhodium complexes that contain a Cp*M-C (M = Ir, Rh) bond stabilised by the intramolecular coordination of neutral donor atoms (N, C, O or P). The formation of metalamacrocycles and cages employing cyclometalated approaches is discussed. In focusing on selected mechanistic insights garnered from iridium/rhodium-catalysed functionalisation of C-H bonds involving cyclometalated complexes, a limited number of substrates will be discussed, but a broad range of mechanistic features is highlighted.

Since the emergence of the concept of chemical topology, interlocked molecular assemblies have graduated from academic curiosities and poorly defined species to become synthetic realities. Coordination-directed synthesis provides powerful, diverse, and increasingly sophisticated protocols for accessing interlocked molecules. Originally, metal ions were employed solely as templates to gather and position building blocks in entwined or threaded arrangements. Recently, metal centers have increasingly featured within the backbones of the integral structural elements, which in turn use noncovalent interactions to self-assemble into intricate topologies. By outlining ingenious recent examples as well as seminal classic cases, this Review focuses on the role of metal−ligand paradigms in assembling molecular links. In addition, the ever-evolving approaches to efficient assembly, the structural features of the resulting architectures, and their prospects for the future are also presented.

Molecular squares obtained from two olefin-bridged bis(NHC) ligands, NHC-Ar-C═C-Ar-NHC, and two Ag(+) or Au(+) ions undergo postsynthetic modifications via a UV-irradiation-initiated [2 + 2] cycloaddition reaction to yield the corresponding cyclobutane-bridged dinuclear tetrakis(NHC) complexes. The tetrakis(NHC) ligand can be liberated from the Ag(I) complexes as the tetraimidazolium salt. For the Au(I) complexes, the substituents at N3 and N3' of the dicarbene ligands determine the outcome of the reaction in the solid state.

Picolyl-functionalized N-heterocyclic carbene complexes have been synthesized by a route involving carbene transfer from Ag(I) carbene precursors. The Ag complexes undergo facile reaction with Ni(PPh 3 ) 2 Cl 2 to yield the carbene complexes Ni(C∧N) 2 Cl 2 (C∧N ) 3-methyl-1-picolylimidazolin-2-ylidene (2a), 3-benzyl-1-picolylimidazolin-2-ylidene (2b)). Complexes 2a,b have been characterized by IR and 1 H and 13 C NMR spectra and elemental analyses. The molecular structures of complexes 2a,b have been confirmed by X-ray single-crystal analyses. The carbene complex 2a shows high catalytic activities of up to 2.6 × 10 7 g of PNB (mol of Ni) -1 h -1 for the addition polymerization of norbornene in the presence of methylaluminoxane (MAO) as cocatalyst and exhibits moderate catalytic activity (3.3 × 10 5 g of PE (mol of Ni) -1 h -1 ) for ethylene polymerization. Catalytic activities, polymer yield, molecular weights, and molecular weight distributions of polynorbornene have been investigated under the various reaction conditions.