Scorpionate complexes

A recent review [440], published 100 years after Werner s coordination theory was first presented, was dedicated to the complex compounds obtained on the basis of polypyrazolyl-borates or scorpionates. Complexes of this kind, an example of which is presented by structure 234, have been obtained with practically all p, /-elements and they can be examined as N-containing analogoues (MN4 coordination unit) of p-diketonates 2 (M04 coordination unit) ... 

Scorpionate Re or Tc trioxides [Tp MOs] (12) (M = Re, Tc) with tridentate hydrotris- and tetrakis(pyrazolyl)-borates and related ligands [Tp = Tp, Tp, B(pz)4 (pzTp) or (Ph)B(pz)3 (PhTp)] are obtained by reaction of M2O7 with the appropriate Na+ or K+ scorpionate salt (XY, Scheme 2) Na[M04] or K[M04] is the other prodnct. They exhibit a distorted octahedral coordination and their chemistry, as well as of the other (mnch less stndied) Re or Tc oxidation state scorpionate complexes, has been reviewed. ... 

Keywords Molecular movements, Metal translocation, Scorpionate complexes, Fluorescence switches, M(III)/M(II) and M(II)/M(I) redox couples... 

Dendronized scorpionate complexes of molybdenum in low and high oxidation state... 

The B-H agostic bond has been reported in few large systems [2, 55] and the computational studies of B-H agostic bond with elaborate methods are therefore rather recent. In a Ru scorpionate complex, the B-H bond of the pyrazolyl borate is found to be at the empty coordination site of the metal centre [56]. The calculated Ru- - -B and Ru- - -H are found to be close to the experimental values despite the fact that the calculated complex has considerably less steric hindrance than the real system (the influence of the steric hindrance will be discussed later). These distances indicate that B and H are... 

Polypyrazolyborate (scorpionate) complexes came onto the scene several years later and several show agostic Mo--H-B interactions. The structure of the Bp ligand in 4, determined in the 1970s, show that is 2.14 A, and the coordinated... 

Two modified scorpionate complexes have been recently synthesized based on the Re(CO)3 fragment. KTp and KTp are synthesized from 3-(4-pyridyl)pyrazole and 3-(2-pyridyl)pyrazole, respectively, and KBH4. Stirring KTp or KTp in the presence of ReCl(CO)5 yields the Re(I) systems Tp" P Re(CO)3 or Tp Re(CO)3. Solid-state structures of both complexes reveal C3 molecular symmetry with geometric features similar to TpRe(CO)3. For Tp" P Re(CO)3, the pyridyl substituents are orthogonal to the pyrazole rings. The pyridyl substituents of Tp Re(CO)3 are twisted 47.4° from the mean plane of the pyrazole ring. ... 

The first solution-based, comproportionation-free, bidirectional OAT to be reported involved the inter-conversion of Tp MoO(K -S2PR2) (7 R = OMe, OEt) and Tp Mo02 K -SP(S)R2 (8) (eqn (7.3)). Similar transformations, involving the R = alkyl derivatives, were subsequently reported by Laugh-lin and Young. Indeed, a large number of scorpionate complexes exhibit... 

Fig. 1 Structure of hydrid scorpionate complex 6 and N-heterocyclic carbine complex 7.

A broader discussion on the use of scorpionate complexes in catalysis is given in Chapter 22. 

Although the mononuclear Cu half-sandwich scorpionate complexes (see above) are commonly less active than the Fe ones, copper complexes can be more effective in multinuclear assemblies (including coordination polymers) and our approach for these species concerns their self-assembly synthesis by using a suitable combination of a metal source, a main chelating ligand, a spacer or linker, apart from a pH regulator. A wide discussion on the types of self-assembied multicopper complexes and their use for alkane functionlization is presented in Chapter 3, and only a very brief overall view is outlined here. 

---