Polypyrazolates of the heavier group 13 and 14 elements: A review

doi:10.1016/j.ica.2009.06.051

Inorganica Chimica Acta

Volume 362, Issue 12, 15 September 2009, Pages 4328-4339

https://doi.org/10.1016/j.ica.2009.06.051 Get rights and content

Abstract

Heavy group 13 and 14 analogs of the poly(pyrazolyl)borates are the subject of this review. Within these, the most extensive research has been performed on the study of polypyrazolylgallates Me₂Ga(R₂pz)₂]⁻ (R = H or Me) and [MeGa(pz)₃]⁻, and their complexes with transition metals. In this review, the common features shared with the boron analogs are presented and contrasted. Other recently reported series of group 13 analogs are the alkali polypyrazolylaluminates Na[(R₂pz)₃ ${AlR}_{3 - n}^{'}$ ] with R = Me, ^tBu; R′ = M. The complexes with one or two pyrazolyl ligands on aluminum display anagostic Al–CH₃⋯Na interactions, these interactions are persistent even if complexes were obtained from solutions with THF that normally coordinate alkali ions. The polypyrazolylsilane ligands Me₂Si(R₂pz)₂ and MeSi(R₂pz)₃ with R = H, Me are remarkably easy to obtain and isolate, in contrast is the fact that the carbon analogs are much harder to obtain and isolate in reasonable yields. Therefore it is surprising that the chemistry of the former ligands is not as developed as could be anticipated. Nevertheless there are examples of the use of these silanes as ligands with the following transition metals: Cr, Mn, Cu, Zn, Sc and Zr. The heavier group 14 analogs with Ge and Sn display coordination patterns with alkali and alkaline ions that resemble those observed with the borates and aluminates. The formation of cationic bimetallic cages of the type [E₂(R₂pz)₃]⁺ and neutral complexes [E₂(R₂pz)₄] has also been observed that can be consider formal isomers of the alkenes. The use of these compounds as ligands has been recently reported.

Graphical abstract

Analogs of the polypyrazolylborate ligand system can be envisioned by replacing the pyrazolyl rings by other substituents or the boron atom for other main group element. The latter variation is the subject of this review and is focused on the polypyrazolates of the heavier 13 and 14 elements.

Introduction

Almost half a century has passed since the introduction of the poly(pyrazolyl)borate ligands by Swiatoslaw Trofimenko, and the number of publications that deals with this ligand system and their complexes continues to grow to date. There are compelling reasons for their enthusiastic use by the scientific community, for instance they are easy to prepare, are robust due to the presence of strong B–H(C), and B–N bonds, are electronically and sterically tunable at convenience with variations of the 3, 4 and 5 positions of the pyrazol rings, and are isolobal with cyclopentadienyl ligands. Analogs of this ligand system can be envisioned by replacing the pyrazolyl rings by other substituents or the boron atom for other main group element [1]. The latter variation is the subject of this review and is focused on the polypyrazolates of the heavier 13 and 14 elements expecting to draw attention to this area of chemistry, which as it will be evident from this contribution is still very undeveloped.

Section snippets

Aluminumpolypyrazolates

Storr and coworkers reported for the first time the synthesis and isolation of polypyrazolylaluminates [Na{Al(pz)₂Me₂}] (1) and [Na{Al(pz)₄}] (2) by the nucleophilic addition of [Na(pz)] to AlMe₃ in THF and subsequent alkane elimination of one and three equivalents of pzH, respectively [2]. The report however, did not give any spectroscopic data for complex 1 and only aluminum analysis information was presented for complex 2.

The first authenticated and structurally characterized example of a

Galliumpolypyrazolates

There is no doubt that the most developed chemistry of polypyrazolates involving heavy Group 13 elements is the one of the gallates informed in a number of publications authored by Storr and coworkers. The general methods to obtain these gallates are depicted in Scheme 3. The monopyrazylylgallate (Scheme 3a) is prepared by nucleophilic addition of sodium pyrazolate to trimethylgallium, then reacted in situ with pyrazole to obtain the bis(pyrazolyl)gallate by alkane elimination (Scheme 3b) [2].

Siliconpolypyrazolates

The chemistry of siliconpolypyrazolates R_nSi(RR′pz)₃₋_n is even more undeveloped than that of the polypyrazolylmethane ligand systems R_nC(RR′pz)₃₋_n, which is unforeseen if considered the better yields of the silicon ligands which are up to 90% in the case of the bis(pyrazolyl)silanes Me₂Si(R₂pz)₂ (R = H 11, Me 12) [30] and the tris(pyrazolyl)silane MeSi(Me₂pz)₃ [31], [32] (13) prepared by simple metathesis reaction of R_nSiCl₃₋_n with $[M (R_{2}^{'} pz)]$ (M = Li or Na) in a hydrocarbon solvent (Eq. (3)) $R_{n} {SiCl}_{3 -}$

Germanium and tinpolypyrazolates

Alkali and alkaline germanium and tin(II) tris-pyrazolates have been prepared by reaction of the pyrazolates E(R₂pz_n) (E = Na, Ba; R = H, Me) with the group 14 dichlorides MCl₂ (M = Ge, Sn) in THF in the appropriate molar ratio as depicted in Scheme 5 [38], [39].

For [(THF)₃Na[μ-pz)₃Ge] (21) (Eq (a), Scheme 5), the [pz₃Ge]⁻ anion acts as a tridentate ligand towards the sodium cation as observed for similar group 13 tris-pyrazolates. Interestingly, in the case of the tin complex [(THF)₂(pzH)Na{μ-pz)₂

Summary

A limited number of complexes in which the boron atom has been replaced for aluminum have been prepared of general formulae [Na{Al(R₂pz)_nMe₃₋_n}] (R = Me, ^tBu). As the number of pyrazolyl rings decrease in these complexes there is a tendency to olygomerization. The olygomers grow at the expense of pyrazolyl binding to sodium ions with different hapticity and Al–CH₃⋯Na interactions. Polypyrazolylgallates and their transition metal complexes are clearly the most extensive family of group 13 and 14

Acknowledgments

The authors gratefully acknowledge CONACyT (Grant U1-54151) for financial support during the preparation of this manuscript.

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Miguel-Ángel Muñoz-Hernández was born in 1968 in Mexico City, Mexico. He was an undergraduate and graduate student at the Universidad Nacional Autónoma de México, UNAM until 1997 when he obtained his Ph.D. degree with Prof. Raymundo Cea-Olivares. Just after graduated he moved to the US as a postdoctoral associate at North Dakota State University and then at the University of Kentucky with Prof. David Atwood from 1997 to 1999. Later in the fall of 1999 joined the faculty of the Center for Chemistry Research at UAEM where he holds a permanent position since 2005. His research interests are focused on the synthesis of organometallic main group complexes as catalysts for different organic transformations and as single-source precursors for the deposition of materials.

Virginia Montiel-Palma was born in 1973 in Mexico City, Mexico, and studied chemistry at the Universidad Nacional Autónoma de México, UNAM. After obtaining her Ph.D. from the University of York, England, under the supervision of Professor Robin Perutz, she moved to the Laboratoire de Chimie de Coordination du CNRS in Toulouse, France for a postdoctoral position with Dr. Sylviane Sabo-Etienne working on transition metal sigma–borane complexes. In 2004 she joined the faculty of UAEM where she now holds a permanent position. Her research interests are in organometallic synthesis with a current focus on transition metal complexes of group 13 elements.

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ReviewPolypyrazolates of the heavier group 13 and 14 elements: A review

Abstract

Graphical abstract

Introduction

Section snippets

Aluminumpolypyrazolates

Galliumpolypyrazolates

Siliconpolypyrazolates

Germanium and tinpolypyrazolates

Summary

Acknowledgments

Organometallics

Organometallics

Chem. Eur. J.

J. Chem. Soc., Chem. Commun.

J. Chem. Soc., Chem. Commun.

J. Chem. Soc., Chem. Commun.

J. Am. Chem. Soc.

J. Am. Chem. Soc.

J. Am. Chem. Soc.

Z. Anorg. Allg. Chem.

Am. Chem. Soc.

Chem. Rev.

Scorpionates: The Coordination Chemistry of Polypyrazolylborates Ligands

J. Chem. Soc., Dalton Trans.

Inorg. Chem. Commun.

Organometallics

Proc. Natl. Acad. Sci. USA

J. Am. Chem. Soc.

Inorg. Chem.

Can. J. Chem.

J. Chem. Soc., Chem. Commun.

J. Chem. Soc., Dalton Trans.

Can. J. Chem.

Can. J. Chem.

Can. J. Chem.

Can. J. Chem.

Can. J. Chem.

Can. J. Chem.

Can. J. Chem.

Organometallics

Can. J. Chem.

Review
Polypyrazolates of the heavier group 13 and 14 elements: A review