Stabilization of coordinatively unsaturated Ir 4 clusters with bulky ligands: A comparative study of chemical and mechanical effects

Alexander Okrut, Oz Gazit, Namal De Silva, Rita Nichiporuk, Andrew Solovyov, Alexander Katz

Research output: Contribution to journalArticlepeer-review


The synthesis and characterization of new cluster compounds represented by the series Ir 4(CO) 12-xL x (L = tert-butyl-calix[4]-arene(OPr) 3(OCH 2PPh 2); x = 2 and 3) is reported using ESI mass spectrometry, NMR spectroscopy, IR spectroscopy and single-crystal X-ray diffraction. Thermally driven decarbonylation of the cluster compound series represented by x = 1-3 according to the formula above is followed via FTIR and NMR spectroscopies, and dynamic light scattering in toluene solution. The propensity of these clusters to decarbonylate in solution is shown to be directly correlated with number density of adsorbed calixarene phosphine ligands and controlled via Pauli repulsion between metal d and CO 5σ orbitals. The tendency for cluster aggregation unintuitively follows a trend that is exactly opposite to the cluster's propensity to decarbonylate. No cluster aggregation is observed for clusters consisting of x = 3, even after extensive decarbonylation via loss of all bridging CO ligands and coordinative unsaturation. Some of the CO lost during thermal treatment via decarbonylation can be rebound to the coordinatively unsaturated cluster consisting of x = 3. In contrast, the clusters consisting of x = 1 and x = 2 both aggregate into large nanoparticles when treated under identical conditions. Clusters in which the calixarene phosphine ligand is replaced with a sterically less demanding PPh 2Me ligand 6 lead to significantly less coordinative unsaturation upon thermal treatment. Altogether, these data support a mechanical model of accessibility in coordinatively unsaturated metal clusters in solution, which hinges on having at least three sterically bulky organic ligands per Ir 4 core.

Original languageEnglish
Pages (from-to)2091-2099
Number of pages9
JournalDalton Transactions
Issue number7
StatePublished - 21 Feb 2012
Externally publishedYes

All Science Journal Classification (ASJC) codes

  • Inorganic Chemistry


Dive into the research topics of 'Stabilization of coordinatively unsaturated Ir 4 clusters with bulky ligands: A comparative study of chemical and mechanical effects'. Together they form a unique fingerprint.

Cite this