Ru–Zn Heterobimetallic Complexes

Project Information

RuZn

Grant agreement ID: 792674

DOI

10.3030/792674

Project closed

EC signature date 15 March 2018

Start date 1 June 2018

End date 31 July 2020

Funded under

• EXCELLENT SCIENCE - Marie Skłodowska-Curie Actions

Total cost

€ 183 454,80

EU contribution

€ 183 454,80

Coordinated by

UNIVERSITY OF BATH
United Kingdom

Periodic Reporting for period 1 - RuZn (Ru–Zn Heterobimetallic Complexes)

Reporting period: 2018-06-01 to 2020-05-31

Summary of the context and overall objectives of the project

One of the main goals of the chemical sciences is to develop novel, better methods for the preparation of organic compounds. These compounds can act as precursors for medicines, agrochemicals and fragrances or become building blocks for the production of polymers and materials. But first, organic molecules should be made in an efficient and sustainable manner. This is often achieved by the means of homogeneous catalysis with metals, a synthetic approach that is widely applied by chemists in both academia and industry. Homogeneous catalysis with metals can be performed by two types of catalysts bearing orthogonal properties: i) derivatives of Lewis Acidic Metals (LAM) and ii) complexes of Late Transition Metals (LTM). The combination of these two types of catalysts in one molecule leads to the heterobimetallic late transition metal – Lewis acidic metal (LTM–LAM) compounds, which have a number of unique properties and are promising for potential catalytic applications, in which they exhibit properties greater than the sum of the two individual parts. However, at this time, LTM–LAM complexes are still significantly underrepresented in chemical research.

In the RuZn project we concentrated our research around a particular group of heterobimetallic complexes, namely ones containing direct unsupported Ru-Zn bonds. The previous work conducted in the group of Prof. Mike Whittlesey (University of Bath, UK; host of the project) showed an intriguing reactivity for several members of this exotic family of molecules, that could be potentially applied to novel catalytic transformations. The objectives for the work of Fedor Miloserdov (the fellow) were to i) develop new synthetic approaches to Ru-Zn complexes, that would allow the synthesis of more compounds of this type bearing different ligand environments, ii) a systematic study of their chemical properties and reactivity and iii) tests of their potential applications as catalysts for the synthesis of organic compounds.

Work performed from the beginning of the project to the end of the period covered by the report and main results achieved so far

Fedor Miloserdov (FMM, the fellow) started his research with the development of novel synthetic routes to unsupported Ru-Zn complexes. The known synthetic protocols required multiple synthetic steps and operations with highly unstable materials. He developed efficient synthetic protocols to novel types of Ru-Zn complexes, starting from ready available and cheap RuHCl and RuCl2-type precursors containing PPh3 as a ligand (Scheme1).

The reactivity of the obtained complexes was studied with an eye on possible catalytic applications. Reactions with a number of selected reagents were performed, and products of the reactions were identified, isolated and characterized. This reactivity study significantly improved the understanding of the nature and behaviour not only of Ru-Zn complexes, but heterobimetallic compounds in general.

Attempts to perform a variety of catalytic transformations with the synthesized Ru-Zn complexes were not fruitful. Following the research risk and contingency plan, FMM focused on the synthesis of other types of heterobimetallic compounds. He developed protocols for novel complexes bearing unconventional Ru-Zn2 and Ru-Zn4 units and studied the reactivity of these systems. Finally, FMM directed studies toward other Ru–M complexes. The first of the metals in each of groups 13 (M = Al) and 14 (M = Sn) were selected for further investigation, and synthetic protocols for the synthesis of corresponding compounds were developed.

The most recently obtained results will be further exploited by the group of Mike Whittlesey (4 projects are currently ongoing). Other results were disseminated in the following publication and presentations at scientific conferences:

List of scientific publications:
1. F. M. Miloserdov,* N. A. Rajabi, J. P. Lowe, M. F. Mahon, S. A. Macgregor* and M. K. Whittlesey*; Zn-Promoted C-H Reductive Elimination and H2 Activation via a Dual Unsaturated Heterobimetallic Ru-Zn Intermediate. J. Am. Chem. Soc. 2020, 142, 6340.
2. N. O'Leary, F. M. Miloserdov,* M. Mahon* and M. K. Whittlesey*; Transforming PPh3 into Bidentate Phosphine Ligands at Ru-Zn Heterobimetallic Complexes. Dalton Trans. 2019, 48, 14000.
3. M. Espinal-Viguri, V. Varela-Izquierdo, F. M. Miloserdov, I. M. Riddlestone, M. F. Mahon* and M. K. Whittlesey*; Heterobimetallic Ruthenium-Zinc Complexes with Bulky N-Heterocyclic Carbenes: Syntheses, Structures and Reactivity. Dalton Trans. 2019, 48, 4176.

List of the scientific conferences:
1. 5th RSC Dalton Division Southern Regional Meeting, Oxford, United Kingdom, September 2019, Oral Presentation.
2. RSC Main Group Chemistry Group Annual Meeting and AGM, London, United Kingdom, September 2019, Poster Presentation.
3. 20th IUPAC International Symposium on Organometallic Chemistry Directed Towards Organic Synthesis, Heidelberg, Germany, July 2019, Poster Presentation.

Progress beyond the state of the art and expected potential impact (including the socio-economic impact and the wider societal implications of the project so far)

It was found that the Ru(PPh3)3HCl-derived Ru-Zn heterobimetallic complex [{Ru(PPh3)(C6H4PPh2)2H}ZnMe] (Fig. 1) undergoes a remarkably efficient H2 activation at -40 oC. In contrast, the corresponding Ru-Li and Ru-Mg compounds all require heating to 60 oC (Scheme 2). The mechanism of the Ru-Zn heterobimetallic cooperativity was studied, which resulted in the formulation of a novel mode of activation of anionic transition metal complexes.

For the reaction of Ru(PPh3)3Cl2 with ZnMe2 a remarkable series of C-H and P-C bond activation, as well as P-C and C-C bond formation steps was observed and the mechanism of this transformation was elucidated. Although the individual steps involved in the overall transformation have been observed separately in previous works, there were no examples in which they have been observed in concert with one another in a single reaction.

Generally speaking, the results obtained over the course of RuZn project represent a significant advancement of knowledge as evident from our high impact journal publication (J. Am. Chem. Soc.). In particular, we significantly improved understanding of cooperativity between Ru with Zn, and developed simple synthetic routes to unconventional Ru-Zn systems. This is expected to eventually contribute to the field to catalysis and become appealing for industrial application to facilitate access to materials, drugs and agrochemicals, which are essential for the goals of the EU Horizon 2020 program. To achieve that, further research is required, which is a part of the general framework of studies in the host group.

Figure 1. Molecular structure of [{Ru(PPh3)(C6H4PPh2)2H}ZnMe]

Scheme 1. Synthesis of Ru-Zn complexes from RuHCl and RuCl2-type precursors

Scheme 2. Ru-Zn heterobimetallic cooperativity in H2 activation.