Group 13 Chemistry - American Chemical Society

Chapter 14

Polyimido Anions of Group 13 Elements Downloaded by UNIV OF CALIFORNIA SAN DIEGO on January 5, 2017 | http://pubs.acs.org Publication Date: June 3, 2002 | doi: 10.1021/bk-2002-0822.ch014

P. Blais, J. K . Brask, T . Chivers, C . Fedorchuk, and G . Schatte Department of Chemistry, University of Calgary, Calgary, Alberta T2N 1N4, Canada

Polyimido anions of the type E(NR)33- (E = B , A l ) are isoelectronic with the common oxo-anions EO33-. This article reviews the unexpected chemistry involved in the attempted synthesis of these trianions by the lithiation of trisamido derivatives of group 13 elements. The reaction of B(NH Bu) with three equivalents of organolithium reagents R L i (R = Me, B u , Bu, Ph) generates the boraamidinates {Li [RB(N Bu) ]} , which have been shown by X-ray crystallography to have dimeric or trimeric cluster structures. The coordination chemistry of the dianionic boraamidinate ligands [RB(NR) ] is reviewed. The reaction of the dimeric trisamido derivatives [M(NH Bu) ] ( M = Al, Ga) with RLi reagents results in the entrapment of monomeric or dimeric organolithium fragments by partially lithiated M N templates. t

3

n

t

t

2

2

x

2

2

t

3

2

2

6

!

2

Polyimido anions with p-block element centres, e.g. [C(N Bu) ] " (1), have attracted attention recently as multidentate ligands with unique electronic and/or stereochemical properties that may engender novel metal-centered chemistry (/, 2). These anions are isoelectronic with common oxo anions, e.g. C 0 " , B 0 " . 3

2

3

© 2002 American Chemical Society

Shapiro and Atwood; Group 13 Chemistry ACS Symposium Series; American Chemical Society: Washington, DC, 2002.

3

3

195

196

3

3

To date, however, the Group 13 analogues of 1, i.e. [B(NR) ] " (2), [A1(NR) ] " (3) etc, have not been reported. 3

Ί

2-

Downloaded by UNIV OF CALIFORNIA SAN DIEGO on January 5, 2017 | http://pubs.acs.org Publication Date: June 3, 2002 | doi: 10.1021/bk-2002-0822.ch014

N'Bu~l I!

NR

3NR I Al

Β

BuN "· Χ Γ

/

N'Bu 1

/

\

RN

3

RN

NR

\ NR

2

Several approaches have been used for the synthesis of polyimido anions of p-block elements (2). The most versatile methods are (a) deprotonation of polyamido complexes (3) (b) transamination reactions (4) and (c) nucleophilic addition to multiply bonded imido complexes (/, 5). For Group 13 systems method (a) is the most promising approach in view of the ready availability of the polyamido precursors B ( N H R ) (6) and [M(NHR) ] [ M = A l (7), G a (8)]. This article describes the interesting chemistry that has resulted from attempts to polylithiate these polyamido complexes. A final section deals with the reactions of primary amines with alkali metal aluminohydrides. 3

3

2

Lithiation of Trisamidoboranes B(NHR)3 l

The reaction of B(NH Bu) with three equivalents of an organolithium reagent R L i gives a mixture of the corresponding boraamidinate {Li [RB(N Bu) ]} and L i N H ' B u (9). 3

t

2

2

x

i

3 L i R + B[N(H)'Bu] -> V {LbfRBCN'Bu^]}* + LiN(H) Bu + 2 R H 3

x

(1)

n

(4a,R = Me; 4b,R = Bu) (4c,R = 'Bu; 4d,R = Ph) In this transformation the organolithium reagent functions as a base to deprotonate two NH*Bu groups of B(NH Bu) and as a nucleophile to displace the third N H B u group as L i N H B u . Aryl boraamidinates have previously been obtained by the dilithiation of bisaminoboranes PhB(NHR') (10). In view of the availability of a wide range of trisaminoboranes B(NHR) (6) and organolithium reagents, this new route to alkyl or aryl boraamidinates is potentially very versatile. f

3

l

f

2

3


197

Structures of Dilithium Alkyl/Aryl Boraamidinates The structures of complexes 4a-d are derived from a simple building block in which an RB unit bridges a distorted four-membered L i N ring (5 in Figure 1). The face-to-face dimerization of two units of 5 generates the ten-atom cluster, with a distorted L i N cube, that has been structurally characterized for 4b, 4c and 4d (9). In the case of 4a a trimeric cluster is also obtained. As indicated in Figure 1 this oligomer is derived from the edge-on (Li-N) interactions of three units of 5 to give a distorted hexagonal prism. It is possible that the use of groups smaller than *Bu attached to nitrogen will result in the formation of larger oligomeric clusters or even polymeric open-ladder structures via lateral Li-N interactions. 2


4

2

4

Figure 1. The monomeric unit 5 and the dimeric and trimeric clusters formed by dilithium alkyl/aryl boraamidinates.

Metal Complexes of Boraamidinates 2

The boraamidinate ligand [RB(NR')2] ~ (6) is isoelectronic with the extensively studied amidinate anions [RC(NR')2]~ (7) (//). Metal complexes of the dianionic ligand 6 are readily obtained by metathetical reactions between Li [PhB(NR) ] and metal halides. Early studies were primarily limited to Group 4 or 14 metals for which complexes containing one or two boraamidinate ligands have been obtained (10b) (Scheme 1). This approach has been extended to the synthesis of the pentafluorophenyl derivative € Ρ Β(Ν Βη) 8ηΜ62 2

2

ι

6

5

2

(10c).



198

Scheme 1.

The metathetical reaction between Li [PhB(N Bu) ] and T e C l in a 2:1 molar ratio produces a spirocyclic tellurium (IV) complex (12) (Scheme 1). More recently we have shown that this reaction produces the boraamidinato tellurium dichloride 8 in excellent yield when a 1:1 molar ratio is employed (13). Subsequent treatment of this dimeric complex with lithium terf-butylamide produces the tellurium imide PhB(^-N Bu) TeN Bu (9) (13). Apparently the boraamidinato ligand inhibits the dimerization of the Te=N*Bu functionality. Complex 9 may also be obtained, though less conveniently, from the reaction of P h B C l with {LbtTeO^Bu^Lb (Scheme 2) (5a). t

2

2

l

4

!

2

2



199

PhB

•Bu N

'Bu ci

'Bu NLi

/

+ TeCl •

\j.

2 LiNH'Bu,

PhB^

N'Bu Te

4

NLi «Bu

N ' tBu 8

N 'Bu

u

L

'Bu^ {^N Te +

'" 'Bu

PhBCl,

Ll Scheme 2.


200

'BU

/

•Bu NLi 2 GaCl

PhB N

PhB.

/

^CI

^Ga

3

THF

NLi •Bu

\

NtBu

[Li(thf) r

''·>,,

4

CI


GaCI, 10

V GaClj 2

l

Li [PhB(N Bu) ] 2

2

THF l

(OEtj) •Bu/^Bu Li [PhB(NGa 1 ^xr 1 I rBul [LiAl(NHR) ] + 4 H

4

2

4

(2)

2

l

(22a, R = Bu) (22b, R = *Pr) (22c,R=/?-tolyl) Complex 22a is also obtained from the reaction of A1C1 with L i N H ' B u (32). Recrystallization from a non-coordinating solvent generates a dimeric species whereas the aryl derivative 22c has been characterized as the ionseparated complex [Li(THF) ][Al(NH/?-tolyl) ] (31). interestingly, the reaction of terr-butylamine with N a A l H in THF yields the bimetallic complex 23. As in the case of 15 monometallation occurs at one of the bridging *BuN(H) groups.


3

4

4

4

l

Bu N(H

'Bu(H)N Al^ ^ ,

/ / t

B

u

(

H

)

B

N

\

^ V / \ (

H

)

u

/

Group 13 Chemistry - American Chemical Society

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