Zn···Zn interactions at nickel and palladium centers† †Electronic supplementary information (ESI) available. CCDC 1478225–1478229. For ESI and crystallographic data in CIF or other electronic format see DOI: 10.1039/c6sc02106a Click here for additional data file

• Published in: Chemical science (Cambridge) 2016-06, Vol.7 (10), p.6413-6421
• Main Authors: Freitag, Kerstin, Molon, Mariusz, Jerabek, Paul, Dilchert, Katharina, Rösler, Christoph, Seidel, Rüdiger W., Gemel, Christian, Frenking, Gernot, Fischer, Roland A.
• Format: Article
• Language: English
• Subjects: Chemistry
• ISSN: 2041-6520; 2041-6539
• DOI: 10.1039/c6sc02106a

Zinc–zinc interactions on nickel and palladium centers are highly dependent on the co-ligands. These dependencies are also found for the formation of dihydrogen vs. dihydride complexes and underline the analogy [Zn 2 Cp* 2 ] ↔ H 2 . The analogy between ZnR fragments and the hydrogen radical represents a fruitful concept in organometallic synthesis. The organozinc( ii ) and -zinc( i ) sources ZnMe 2 (Me = methyl) and [Zn 2 Cp* 2 ] (Cp* = pentamethylcyclopentadienyl) provide one-electron fragments ·ZnR (R = Me, Cp*), which can be trapped by transition metal complexes [L a M], yielding [L b (ZnR) n ]. The addition of the dizinc compound [Zn 2 Cp* 2 ] to coordinatively unsaturated [L a M] by the homolytic cleavage of the Zn–Zn bond can be compared to the classic oxidative addition reaction of H 2 , forming dihydride complexes [L a M(H) 2 ]. It has also been widely shown that dihydrogen coordinates under preservation of the H–H bond in the case of certain electronic properties of the transition metal fragment. The σ-aromatic triangular clusters [Zn 3 Cp* 3 ] + and [Zn 2 CuCp* 3 ] may be regarded as the first indication of this so far unknown, side-on coordination mode of [Zn 2 Cp* 2 ]. With this background in mind the question arises if a series of complexes featuring the Zn 2 M structural motif can be prepared exhibiting a (more or less) intact Zn–Zn interaction, i.e. di-zinc complexes which are analogous to non-classical dihydrogen complexes of the Kubas type. In order to probe this idea, a series of interrelated organozinc nickel and palladium complexes and clusters were synthesized and characterized as model compounds: [Ni(ZnCp*)(ZnMe)(PMe 3 ) 3 ] ( 1 ), [Ni(ZnCp*) 2 (ZnMe) 2 (PMe 3 ) 2 ] ( 2 ), [{Ni(CN t Bu) 2 (μ 2 -ZnCp*)(μ 2 -ZnMe)} 2 ] ( 3 ), [Pd(ZnCp*) 4 (CN t Bu) 2 ] ( 4 ) and [Pd 3 Zn 6 (PCy 3 ) 2 (Cp*) 4 ] ( 5 ). The dependence of Zn···Zn interactions as a function of the ligand environments and the metal centers was studied. Experimental X-ray crystallographic structural data and DFT calculations support the analogy between dihydrogen and dizinc transition metal complexes.