Bifunctional Cp∩N Complexes—Unusual Structural Features and Electronic Coupling in Highly Preorganized Bimetallic Systems

Abstract

Dedicated to Professor Lutz F. Tietze on the occasion of his 60th birthdayComplexes of cyclopentadienyl (Cp) ligands with functional amino or amido side chains are currently receiving enormous attention in organometallic chemistry. [1,2] While the donor substituent tethered to the Cp moiety usually serves a hemilabile chelate function in generic type A complexes, we recently put forward a novel approach in which a pyrazolate group in complexes of type B links two Cp units and acts both as an intramolecular N donor and as a bridging group spanning two metal ions . [3] Such a strategy, that is the formal coupling of two N-containing ligand compartments through a functionalized pyrazolate bridge to constitute a preorganized dinuclear scaffold, has successfully been employed for mimicking cooperative effects in biomimetic coordination compounds. [4] Accordingly, type B systems are now expected to give rise to novel organometallic chemistry in which two adjacent metal ions might work in concert. Here we report the first transition metal complex of type B, its unusual structural features in the solid state, and characteristics of the metal ± metal interaction in the mixed-valent form.It proved difficult to introduce the parent Cp into the side arms of functionalized pyrazole derivatives such as 1, [5] and thus we employed a ™protected∫ form of Cp: attachment of [CpMn(CO) 3 ] to the pyrazole nucleus was achieved in a [Pd(PPh 3 ) 2 ]/ZnCl 2 -catalyzed cross-coupling reaction [6] yielding 2 (Scheme 1).A single-crystal structure analysis [7] showed that 2 contains a protonated (noncoordinating) 1H-pyrazole heterocycle suitably arranged to potentially interact with the pendant Scheme 1. Synthesis of the complex K 3 À . metal carbonyl fragments. Photolytic decarbonylation of 2 and deprotonation using KOtBu gave K 3 À , the first bimetallic complex of type B. Its formation can be monitored by IR spectroscopy through the characteristic changes of the CO stretching frequencies (2015/1927 cm À1 for 2 versus 1919(1896)/1848(1816) cm À1 for 3 À ). [8] Single crystals of K 3 À ¥ 0.9 THF obtained from THF/light petroleum were analyzed by X-ray crystallography. [9] The asymmetric unit contains four (very similar) dimanganese(i) units of the anticipated constitution-one of which is depicted in Figure 1. The N-Mn-C CO angles in 3 À are rather large (mean value 101.98) compared to those in other [CpMn(CO) 2 L] complexes (L N-donor ligand; 92.6 ± 98.18 according to a CSD search), indicating a somewhat strained situation in the chelate complex 3 À . Figure 1. Molecular structure of 3 À (30 % probability ellipsoids). Selected interatomic distances [ä] and range of selected bond angles and dihedral angles [8]; values for the other three independent molecules in square brackets: Mn1-N1 2.

Synthesis and structural characterization of unsymmetrical osmocenes containing the pentamethylcyclopentadienyl ligand

“…Os(1)-C(1) 2.168(2) Os(1)-C (2) 2.177(2) Os(1)-C (3) 2.166(2) Os(1)-C(4) 2.172(2) Os(1)-C (5) 2.158(2) Os(1)-C (11) 2.238(2) Os(1)-C (16) 2.233 (2) Os (1)-C(17) 2.195(2) Os(1)-C (18) 2.246(2) Os(1)-C (19) 2.237(2) Os(1)-C 5 Me 5 centroid 1.788(2) Os(1)-fluorenyl centroid 1.861(2) C 5 Me 5 -Os(1)-fluorenyl centroid 178.7(1) Table 5 Selected bond lengths (Å ) and angles (°) for 4…”

Ligand Protonation Triggers H2 Release from a Dinickel Dihydride Complex to Give a Doubly “T”‐Shaped Dinickel(I) Metallodiradical

“…Comparison of the molecular structures of K[LNi I 2 ] ( 2 K ) and K[L(Ni II ‐H) 2 ] ( 1 K ) shows that the most conspicuous difference is the position of the K + cation: In 1 K the K + is located within the plane defined by the pyrazolate‐bridged dinickel dihydride core and in between the two flanking aryl rings of the 2,6‐disopropylphenyl (dipp) substituents at distances indicative of cation‐π interactions [18a] . In contrast, in 2 K the K + is located above the pyrazolate [20] and is additionally ligated by four THF molecules (the structure of 2 Na is very similar, but the Na + has only two THF ligands; Figure S9). This striking difference may reflect attractive K + ⋅⋅⋅hydride interactions in 1 K that are now absent in the double “T”‐shaped dinickel(I) complex 2 K , in line with the stabilizing role of K + with respect to H 2 elimination from 1 K which has a much higher activation barrier than H 2 elimination from 1′ .…”

A Series of [2+2] Schiff Base Macrocyclic Dinuclear ZnII Complexes with Rigid 1,2‐Diamine and Flexible 1,8‐Diamine Components

“…There have been extensive studies in the field of Schiff base macrocyclic complexes since they were first reported more than 40 years ago because of their particular properties and potential applications in the fields of magnetism, catalysis, artificial receptors, biological activities, and so on. Up to now, metal‐free and metal‐ion template methods have been used to prepare a variety of macrocyclic Schiff base metal complexes, but the latter method has proved more effective .…”