β-Diketiminate-Stabilized Magnesium(I) Dimers and Magnesium(II) Hydride Complexes: Synthesis, Characterization, Adduct Formation, and Reactivity Studies

DOI: 10.1002/chem.200902425

b-Diketiminate-Stabilized Magnesium(I) Dimers and Magnesium(II)

Hydride Complexes: Synthesis, Characterization, Adduct Formation, and

Reactivity Studies

Simon J. Bonyhady,^[a]Cameron Jones,*^[a]Sharanappa Nembenna,^[a]Andreas Stasch,*^[a]

Alison J. Edwards,^[b]and Garry J. McIntyre^[c]

Abstract: The preparation and charac-

terization of a series of magnesium(II)

iodide complexes incorporating b-dike-

timinate ligands of varying steric bulk

led to the magnesi

[(^MesNacnac)MgMg ^MesNacnac)]

[(^tBuNacnac)MgMg(^tBuNacnac)]. The re-

G

[(^MesNacnac)Mg(L)Mg(L)(^MesNacnac)]

E

(L=THF or DMAP), [(^MesNacnac)Mg-

AHCTUNGTRENNUNG

(m-AdN₆Ad)Mg(^MesNacnac)] (Ad=1-

duction of

[(^DippNacnac)MgI

[(^MesNacnac)

MgI

um gave a low yield of the crystallo-

graphically characterized complex

[(^DippNacnac)Mg (m-I)Mg(^MesNac-

(m-H)

nac)]. All attempts to form berylli-

a

1:1 mixture of

adamantyl),

N₆Ad)Mg(^tBuNacnac)],

[(^MesNacnac)

Mg(m-tBu₂N₂C₂O₂)Mg-

^MesNacnac)] and revealed that, in gen-

[(^tBuNacnac)Mg

ACHTUNGTRENNUNG

and

denticity,

namely,

[(ArNC-

ACTHNUTRGEN(UGN OEt₂)] and

Me)₂CH]^ꢀ(Ar=phenyl, (^PhNacnac),

mesityl (^MesNacnac), or 2,6-diisopropyl-

phenyl (Dipp, ^DippNacnac)), [(DippNC-

A

R

ACHTUNGTRENNUNG

AHCTUNGTRENNUNG(

eral, the reactivity of the magnesium(I)

dimers is inversely proportional to

their steric bulk. The preparation and

tBu)₂CH]^ꢀ

(

^tBuNacnac), and [(DippNC-

A

ACHTUNGTRENNUNG

Me)(Me₂NCH₂CH₂NCMe)CH]^ꢀ

^DmedaNacnac) are reported. The com-

ACHTUNGTRENNUNG

(

A

characterization of [(^tBuNacnac)Mg

ACHTUNGTRENNUNG(m-

plexes

[(^MesNacnac)MgI

nac)MgI(OEt₂)],

[(^PhNacnac)MgI

(OEt₂)],

tions

[{(^DippNacnac)

[{(^tBuNacnac)

CaI

[(^MesNacnac)BeI],

ACHTNUTRGNEUGN(OEt₂)}₂], or

H)₂Mg(^tBuNacnac)] has shown the com-

pound to have different structural and

physical properties to [(^tBuNacnac)-

(OEt₂)],

[(^DmedaNac-

T

G

[(^MesNacnac)MgI-

E

A

been unsuccessful. The further reactivi-

ty of the magnesium(I) complexes

MgMg(^tBuNacnac)]. Treatment of the

ACHTUNGTRENNUNG

C

[(^tBuNacnac)MgI-

former with DMAP has given

E

[(^MesNacnac)MgMg(^MesNacnac)]

and

[(^tBuNacnac)Mg(H)

ACHTUNGTRENNUNG

pyridine) were shown to be monomeric

by X-ray crystallography. In addition,

the related b-diketiminato beryllium

[(^tBuNacnac)MgMg(^tBuNacnac)] towards

a variety of Lewis bases and unsaturat-

ed organic substrates was explored.

These studies led to the complexes

ray crystal structure of which disclosed

it to be the first structurally authenti-

cated terminal magnesium hydride

complex. Although attempts to prepare

and

[(^MesNacnac)BeI] and [{(^DippNacnac)-

CaI(OEt₂)}₂] were prepared and crys-

calcium

iodide

complexes,

[(^MesNacnac)Mg ^MesNacnac)]

ACTHNUTRGNNEG(U m-H)₂MgACHTUTGNRENNUN(G

A

U

were not successful, a neutron diffrac-

tion study of the corresponding magne-

sium(I) complex, [(^MesNacnac)Mg-

Keywords: low oxidation state

·

tallographically characterized. The re-

ductions of all metal(II) iodide com-

plexes by using various reagents were

attempted. In two cases these reactions

magnesium hydrides · magnesium ·

metal–metal interactions

diffraction

· X-ray

AHCTUNGTRENNUNG

Mg(^MesNacnac)] confirmed that the

compound is devoid of hydride ligands.

[a] S. J. Bonyhady, Prof. C. Jones, Dr. S. Nembenna, Dr. A. Stasch

School of Chemistry, Monash University

PO Box 23, Melbourne, VIC, 3800 (Australia)

Fax : (+61)3-9905-4597

[b] Dr. A. J. Edwards

Bragg Institute

Australian Nuclear Science and Technology Organisation

PMB1, Menai, N.S.W. 2234 (Australia)

E-mail: cameron.jones@sci.monash.edu.au

andreas.stasch@sci.monash.edu.au

[c] Dr. G. J. McIntyre

Institut Laue-Langevin, 6 rue Jules Horowitz

BP 156, 38042 Grenoble Cedex 9 (France)

Supporting information for this article is available on the WWW

under http://dx.doi.org/10.1002/chem.200902425.

938

ꢀ 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Chem. Eur. J. 2010, 16, 938 – 955

FULL PAPER

Introduction

the metal centers of 2, the magnesium(II) hydride complex

ACTHNUTRGNEUNG

[(^DippNacnac)Mg(m-H)₂Mg(^DippNacnac)] (3) was prepared

The chemistry of the Group 2 elements is dominated by the

+2 oxidation state so much so that until late 2007 no struc-

turally characterized examples of molecular compounds of

these elements were known to exist under normal laborato-

ry conditions with the metal in the +1 oxidation state. This

is perhaps surprising considering the rapid expansion of the

chemistry of compounds containing p-block elements in

very low oxidation states in recent decades.^[1]That is not to

say that low-oxidation-state Group 2 complexes were not

known to be capable of existence under extreme conditions.

In the case of magnesium, this has been proven by the spec-

troscopic characterization of monomeric magnesium(I) com-

pounds such as Mg^I(NC) in deep space.^[2]In addition, a

number of monomeric and dimeric magnesium(I) com-

pounds such as XMgMgX and MgX (X=H or Cl) have

been prepared and spectroscopically studied under matrix

isolation conditions,^[3,4]whereas the existence of cluster

compounds that have the general formula RMg₄X (X=

halide) has been suggested by mass spectrometry experi-

ments.^[5]Moreover, a variety of theoretical investigations of

compounds of the type RMMR (M=Be, Mg or Ca; R=

alkyl, aryl, amide etc.,)^[6]have concluded that the strength

and was shown to have very different physical and chemical

properties.^[13]

An experimental charge density study of 2 has recently

confirmed the covalent nature of the metal–metal interac-

tion in that compound,^[14]but the study indicated that the

electron density between the magnesium centers is rather

diffuse. It is thought that this diffuseness is the major cause

ꢀ

behind the exceptional elongation (by>0.2 ꢁ) of its Mg

Mg bond upon formation of the Lewis base adducts

[(^DippNacnac)Mg(L)Mg(L)(^DippNacnac)] (4; L=THF, diox-

ane, 4-tert-butylpyridine or 4-dimethylaminopyridine

(DMAP)). This is despite the apparent weakness of the L!

Mg bonds, at least in the case of the ether adducts, which

readily and rapidly lose their coordinated ether molecules

when placed in vacuo. Note that a related adduct of the

magnesium(II) hydride complex 3, namely, [(^DippNacnac)Mg-

(thf)(^DippNacnac)], has been reported and

AHCTUNTGREU(NGNN thf)ACHTUNGTREG(NNUN m-H)₂MgACHTNGUTRENNGUN

shown to have distinctly different properties to those of 4

(L=THF).^[13]Comparisons of the reactivity of the magne-

sium(I) dimer, 2, and its magnesium(II) hydride counterpart,

3, towards N-functionalized unsaturated substrates have also

been carried out.^[15]These have revealed 2 to act as a facile

two-center/two-electron reductant towards the substrates,

whereas 3 generally behaves as a hydromagnesiation re-

agent. In each case it is thought that the reaction mechanism

involves initial coordination of the substrate at the magnesi-

um centers of the reactant prior to its reduction or hydro-

magnesiation.

ꢀ

of their M M bonds is not insignificant, and that examples

that are stable under ambient conditions might be accessible

if sufficiently bulky ligands (R) are employed.

In 2004, Carmona et al. prepared the first structurally

characterized example of a dimeric zinc(I) compound,

Cp*ZnZnCp* (Cp*=C₅Me₅).^[7,8]Since this initial report,

more than half a dozen other examples have been prepared

and their chemistry has begun to be developed.^[8,9]Mindful

of the chemical similarities between zinc and magnesium,

Recently, an extension of the chemistry of magnesium(I)

dimers that are stable under ambient conditions has been re-

alized with the preparation of the ion-pair complex, [K-

and the calculated stability of Mg Mg bonded dimers, we

(DAB)] (DAB=[(DippNCMe)₂]^2ꢀ).^[16]

ACHTUNGTRENU(GNN thf)₃]₂ACHTUNREGTG[NNUN (DAB)MgMgACHTNUGTRENNUGN

ꢀ

2+

investigated the preparation of such compounds by the po-

tassium metal reductions of the guanidinate or b-diketimi-

nate chelated magnesium(II) precursor complexes

In this complex, the Mg₂core is coordinated by two di-

ꢀ

G

nificantly longer (2.9370(18) ꢁ) than those of 1 or 2. DFT

calculations on a model complex revealed this s bond to

have considerable p character (55%) as opposed to the pre-

dominantly s-character bonds of 1 and 2. Moreover, whereas

2 readily forms adducts with a range of Lewis bases, the

(Priso)] and [(^DippNacnac)MgI-

[(Priso)MgACHTUNGTRENNUNG(m-I)₂MgACHTUNGTRENNUNG(OEt₂)ACHTNUGTRENNGUN

ACHTUNGTRENNUNG

(OEt₂)] (Priso=[(DippN)₂CNiPr₂]^ꢀ, ^DippNacnac=[(DippNC-

Me)₂CH]^ꢀ, Dipp=C₆H₃iPr₂-2,6), respectively. These afford-

ed the remarkably thermally stable magnesium(I) dimer

complexes [(Priso)MgMg

G

magnesium centers of [KACHTNUTGREGU(NNN thf)₃]₂AHCTUNRTGENNG[UN (DAB)MgMgACHTNUGTRNE(NUGN DAB)] do

and [(^DippNacnac)MgMg(^DippNacnac)] (2, decomposes>

not coordinate THF. To date there are no known N,N’-che-

lated beryllium(I) or calcium(I) dimers (such as 1 and 2),

but the synthesis of the thermally stable, paramagnetic cal-

cium(I) inverse sandwich complex [(thf)₃Ca{m-C₆H₃Ph₃-

3008C).^[10,11]X-ray crystallographic studies of both com-

pounds revealed them to have Mg Mg distances of approxi-

mately 2.85 ꢁ, that is, slightly longer than the sum of two di-

valent magnesium covalent radii (2.82 ꢁ).^[12]Calculations on

models of these compounds suggest that they contain cova-

1,3,5}CaACTHNUTRGNEUNG

(thf)₃] gave hope that this may be achieved.^[17]

In this paper, we describe efforts to extend the known

chemistry of b-diketiminate coordinated magnesium(I)

dimers and magnesium(II) hydrides to complexes incorpo-

rating a range of ligands of varying steric bulk and denticity.

The preparation of precursors to these complexes, the re-

ductions of the precursors, and the further reactivity of the

target magnesium(I) complexes towards Lewis bases and/or

unsaturated substrates, for example, will be discussed. In ad-

2+

lently bonded Mg₂cores (with bond dissociation energies

of approximately 45 kcalmol^ꢀ1) that have largely ionic inter-

actions with their ligands.^[3a,10,13]The Mg Mg bonds of the

cores are associated with the HOMOs of the models and

have high s character, which had been previously calculated

ꢀ

for other Mg Mg bonded dimers. The lowest two metal-

based unoccupied orbitals of the models are close to degen-

erate and have what is essentially p-bonding character. To

definitively prove the absence of hydride ligands that bridge

ꢀ

dition, although not successful, attempts to prepare Be Be

ꢀ

and Ca Ca bonded complexes will be discussed.

Chem. Eur. J. 2010, 16, 938 – 955

ꢀ 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

www.chemeurj.org

939

C. Jones, A. Stasch et al.

Results and Discussion

characterized [Eq. (3)]. Moreover, the ability of the mono-

meric compound 9 to accept coordination from Lewis bases

was demonstrated by its treatment with DMAP, which gave

Preparation and characterization of Group 2 metal(II)

iodide precursor complexes: The high thermal stability of

compound 2 is no doubt derived from the kinetic protection

provided by its bulky ^DippNacnac ligands. To evaluate the im-

portance of this protection, a series of related magnesium(I)

compounds that contain chelating b-diketiminate ligands of

lesser or greater steric bulk than ^DippNacnac were targeted.

In addition, considering that the Lewis base adducts of 2

(i.e., the four-coordinate complexes 4) are stable up to

2508C (for L=4-tert-butylpyridine),^[13]the preparation of a

four-coordinate, intramolecularly base-stabilized analogue

of 2 incorporating a functionalized b-diketiminate was an

objective of this study. The ligands that were chosen for

these purposes were [(ArNCR)₂CH]^ꢀR=Me, Ar=phenyl

the complex [(^tBuNacnac)MgI

ACTHNUTRGNEUNG(DMAP)] (12) [Eq. (3)].

ꢀ

To explore the possibility of preparing Be Be and Ca Ca

bonded complexes, potential precursors to examples of such

compounds, [(^MesNacnac)BeI] (13) and [{(^DippNacnac)CaI-

AHCTUNTGRENNG(UN OEt₂)}₂] (14), were synthesized by treatment of the potassi-

um salt of the b-diketiminate with MI₂(M=Be or Ca) in a

diethyl ether/toluene mixture or neat diethyl ether, respec-

tively, as shown in [Eq. (4)] and [Eq. (5)]. In line with the

(^PhNacnac) or mesityl

(

^MesNacnac); R=tBu, Ar=Dipp

(

^tBuNacnac); and [(DippNCMe)(Me₂NCH₂CH₂NCMe)CH]^ꢀ

^DmedaNacnac).

Considering that compound 2 is prepared in over 50%

yield through the reduction of the corresponding magnesi-

A

ACHTUNGTRENNUNG

complexes involving the above-mentioned ligands were seen

as appropriate precursors to the target magnesium(I)

dimers. Although [(^DippNacnac)MgI

ACTHNUTRGEN(UNG OEt₂)] was previously

prepared by the treatment of [Li(^DippNacnac)] with commer-

cially available MgI₂,^[18]more convenient routes to this and

related compounds have been developed in our laboratory.

Good isolated yields of [(^DippNacnac)MgI

ACHTUNGTRENNUNG

[(^PhNacnac)MgI

G

E

difference in the covalent radii of the Group 2 metals (Be=

0.96 ꢁ, Mg=1.41 ꢁ, Ca=1.76 ꢁ),^[12,19]the beryllium com-

plex is an unsolvated three-coordinate monomer, whereas

the calcium complex is a solvated five-coordinate iodide-

bridged dimer. This is despite the greater steric bulk of the

b-diketiminate ligand in 14. Both can be compared to the

related monomeric, four-coordinate, ether solvated magnesi-

um complexes 5–8.

AHCTUNGTRENNUNG

through deprotonation of the appropriate b-diketimine with

MeMgI in diethyl ether as described in [Eq. (1)]. This

The spectroscopic data for complexes 6–14 are consistent

with their proposed formulations. In all cases, X-ray crystal-

lographic studies were used to authenticate the structures of

the complexes. ORTEP diagrams for compounds 7–9, 13,

and 14 are depicted in Figure 1 and selected metrical param-

eters for all compounds are collected in Table 1. Compounds

6 and 7 possess distorted tetrahedral magnesium geometries,

and have very similar structures to that previously reported

for 5.^[18]Compound 8 is monomeric and its magnesium

center has a distorted square-pyramidal geometry with the

ether ligand in the apical position. Not surprisingly, the di-

methylamino nitrogen center is significantly more distant

from the Mg atom than either nitrogen center of the b-dike-

timinate fragment of the ligand. In contrast, the magnesium

center of monomeric 9 has a distorted trigonal-planar geom-

method is not appropriate for ^tBuNacnacH, which does not

react with the Grignard reagent in boiling diethyl ether over

extended periods. Alternatively, ^tBuNacnacH can be depro-

tonated when it is heated at 1008C with dibutylmagnesium

in toluene for 16 h. The complex that was generated in situ,

[(^tBuNacnac)MgnBu], was then allowed to react with one

equivalent of I₂, to give a good yield of [(^tBuNacnac)MgI] (9)

after work-up [Eq. (2)]. We have generally found that the

ether ligands of 5–8 are readily replaced by THF by dissolv-

ing the complexes in that solvent. In the cases of the reac-

tions with 5 and 7, the products [(^DippNacnac)MgI

and [(^MesNacnac)MgI

(thf)] (11), respectively, have been fully

ACHTUNGTRENUN(NG thf)] (10)

AHCTUNGTRENNUNG

ꢀ

etry with shorter N Mg and Mg I distances than in any of

the other complexes. The presence of tert-butyl substituents

on the backbone of the ligand has the effect of pushing its

Dipp substituents towards the magnesium atom, thus pre-

venting dimerization of the molecule (such as in the dimeric

940

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ꢀ 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Chem. Eur. J. 2010, 16, 938 – 955

Stabilized Mg^IDimers and Mg^IIHydride Complexes

FULL PAPER

Figure 1. Thermal ellipsoid (25%) drawings of 7–9, 13, and 14. Hydrogen atoms are omitted for clarity. Only one of the two crystallographically inde-

pendent molecules of 7 is shown. Selected metrical parameters for these compounds, as well as for 6 and 10–12 are given in Table 1. Symmetry transfor-

mations (’) for 13: ꢀx, y, ꢀz+1/2; 14: 1ꢀx, ꢀy, ꢀz.

Table 1. Selected interatomic distances [ꢁ] and angles [8] for 6–14.

6

7

8

9

10

11

12

13

14

ꢀ

M N

2.022(2)

2.023(2)

–

2.004(2)

2.670(1)

2.031(2)

2.036(2)

–

2.019(2)

2.6915(9)

2.118(2)

2.095(16)

2.270(2)^[b]

2.064(2)

2.827(1)

1.990(2)

1.991(2)

–

2.038(3)

2.041(3)

–

2.039(3)

2.651(1)

2.026(2)

2.036(2)

–

2.024(2)

2.662(1)

–

2.038(3)

2.049(4)

2.112(4)^[b]

–

2.672(1)

–

1.600(2)

–

2.296(2)

–

111.8(2)

2.347(2)

2.367(2)

–

2.378(2)

3.1224(8)

3.090(1)

81.34(8)

ꢀ

M O

–

ꢀ

M I

2.597(1)

N-M-N^[a]

94.19(6)

92.80(7)

87.84(6)

97.11(6)

95.3(1)

92.97(9)

98.1(1)

[a] Angle associated with both b-diketiminate nitrogen centers. [b] Distance associated with the -NMe₂or DMAP nitrogen center.

complex [(^DippNacnac)Mg

Br^[20]). This distortion is mani

G

trigonal-planar metal center. Both Be N distances of the

compound (1.600(2) ꢁ) are at the short end of the reported

ꢀ

AHCTUNGTRENNUNG

actions in the molecule (2.830 ꢁ mean) compared with

range (1.502–1.943 ꢁ),^[21]whereas the Be I distance

ꢀ

those in [(^DippNacnac)MgI

G

(2.296(2) ꢁ) is significantly shorter than those in the only

other structurally characterized compound that contains a

ample.^[18]

The molecular structure of the beryllium complex 13 is re-

lated to that of 9 in that it is monomeric with a distorted

Be I bond, [BeI

compound 14 is dimeric in the solid state with iodide ligands

(OEt₂)₂] (2.412 ꢁ mean).^[22]In contrast,

₂ACHTUNGTRENNUNG

ꢀ

Chem. Eur. J. 2010, 16, 938 – 955

ꢀ 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

www.chemeurj.org

941

C. Jones, A. Stasch et al.

bridging the heavily distorted trigonal bipyramidal calcium

centers (such as in the dimeric structures of

[{(^DippNacnac)Ca (m-X)}₂] X=F^[23]or Cl^[24]).

ACHTUNGTRENNUNG(thf)ACHTUTGNRENNUGN

Reductions of Group 2 metal(II) iodide precursor com-

plexes: Previously we have shown that the reduction of 5

with an excess of potassium metal in toluene over 24 h gives

a moderate yield of the yellow magnesium dimer 2.^[10]When

the reaction was carried out by using sodium metal as the

reducing agent, a similar yield (ca. 50%) of 2 could be re-

covered after 5–7 days. Reduction of the closely related

THF adduct 10 with sodium in toluene does give 2, but in

reduced yields. Note that when an approximately 1:40 mix-

ture of diethyl ether/toluene is used as the solvent, these re-

ductions proceed more rapidly and with similar yields. It is

thought that the presence of small amounts of the ether

helps to dissolve the precursor. To test the facility of other

of products. Both 16 (m.p. 201–2038C) and 17 (m.p. 278–

2808C) are very thermally stable in the solid state, and tolu-

ene solutions of the compounds can be stored for weeks at

258C without showing signs of decomposition. Although the

sodium or potassium reductions of the five-coordinate pre-

cursor 8 led to red-orange solutions (such as for the red-

orange magnesium(I) adduct complexes 4),^[13]no identifiable

magnesium-containing products were isolated from the reac-

tion mixtures. Instead, the only product that was isolated

from the reaction with potassium, and in very low yield, was

[{K(^DmedaNacnac)}₆], which

a poor-quality X-ray crystal

structure revealed to be hexameric in the solid state. No fur-

ther efforts were made to reduce compound 8.

reducing reagents,

5 was allowed to react with KC₈

(1.2 equivalents) in toluene, or with an excess of freshly

filed calcium metal in toluene. The former reaction led to

low isolated yields of unreacted 5 and [K(^DippNacnac)], a

moderate yield of 2, and a mixture of other products. This

suggests that KC₈is a less controllable reducing reagent

than potassium metal (at least in the reduction of 5), and

that it can lead to over reduction of the magnesium(II) pre-

cursor. In contrast, no reaction was observed between 5 and

the milder reducing agent, calcium metal.

To shed light on the mechanisms and kinetics of the reac-

tions that gave the magnesium(I) dimers 2, 16, and 17, two

co-reduction experiments were carried out. In the first, an

equimolar mixture of 9 and 5 was treated with an excess of

potassium in toluene at 258C. After stirring for one day, a

¹H NMR spectrum of an aliquot of the mixture was ob-

tained. This revealed the consumption of both starting mate-

rials and the predominant formation of 2 and 17. Resonan-

ces for several other products were observed in the spec-

trum, although none of these could be confidently identified

or isolated from the reaction mixture. Accordingly, another

co-reduction reaction of equimolar amounts of 5 and 7 was

carried out by treatment of the mixture with an excess of

potassium in toluene. The reaction was stopped after 24 h

and work-up of the reaction mixture gave a low isolated

yield of the unusual mixed-ligand hydride/iodide-bridged

Armed with the knowledge gained from the various reac-

tions that gave 2, the development of synthetic protocols to

access magnesium(I) compounds derived from the precursor

complexes 6–9 was initiated. The only product that was iso-

lated, in low yield, from the reductions of 6 with either po-

tassium or sodium metal in toluene was the homoleptic

complex [MgACHTUNGTRENNUNG

(^PhNacnac)₂] (15), which was spectroscopically

and crystallographically characterized. It is possible that the

intermediate in this reaction was the target dimer

product [(^DippNacnac)Mg (m-I)Mg(^MesNacnac)] (18) as

ACTHNGUTRENNU(G m-H)ACHTUGNTRENNNUG

shown in [Eq. (8)]. At this stage it is not known what the

ACHTUNGTRENNUNG

[(^PhNacnac)MgMg(^PhNacnac)], but because of the sterically

unhindered nature of its b-diketiminate ligand it dispropor-

tionates to 15 and magnesium metal under the reaction con-

ditions employed. More success was achieved with the bulki-

er precursor 7, the sodium reduction of which, after five

days, reproducibly gave the pale-yellow magnesium(I) com-

pound 16 in yields greater than 50% [Eq. (6)]. Interestingly,

other products of the reaction are, although the absence of

significant amounts of 2 and 16 in the mixture possibly indi-

cates that the reductions of 5 and 7 proceed at similar rates.

What is of most interest, however, is the presence of a hy-

dride ligand in 18. This most likely results from hydrogen

abstraction from the toluene solvent or magnesium-coordi-

nated diethyl ether. Such processes are commonly observed

in alkali-metal reductions of main group element halide

complexes.^[25]

The formation of compound 18 raised the question as to

whether magnesium hydride complexes are by-products in

the formation of 2, 16, and 17. To probe this, aliquots were

taken just prior to work-up from standard reduction reac-

reduction of this precursor with potassium metal also affords

16, but only in very low isolated yields (ca. 2–5%). In con-

trast, reaction of the much bulkier precursor 9 with an

excess of potassium in toluene gave a good yield of the

orange magnesium(I) dimer, [(^tBuNacnac)MgMg(^tBuNacnac)]

(17) after crystallization from toluene [Eq. (7)]. A different

outcome resulted from the treatment of 12 with potassium

in toluene, namely, the formation of an intractable mixture

942

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Chem. Eur. J. 2010, 16, 938 – 955

Stabilized Mg^IDimers and Mg^IIHydride Complexes

FULL PAPER

tion mixtures that gave these compounds. After removal of

volatiles from the aliquots and dissolution of the residues in

[D₆]benzene, analyses were carried out by ¹H NMR spec-

troscopy. The reaction mixture that gave 17 contained no

obvious magnesium hydride compounds or any other signifi-

cant by-product. In contrast, the mixture that afforded the

less kinetically protected complex 16 comprised an approxi-

mately 75:25 mixture of 16 and the homoleptic complex,

[Mg(^MesNacnac)₂] (19). Other than small amounts of uniden-

tified products in the reaction mixture that gave 2, the mag-

nesium hydride complex 3 was also found to be present in

significant amounts (ca. 15%) as determined by integration

of its characteristic hydride resonance at d=4.03 ppm. Of

further note is the presence of another hydride resonance in

the spectrum at d=4.00 ppm, the integration of which is ap-

proximately half the value of the former. It is possible that

attempted. However, even when this mixture was heated in

a sealed tube at 1008C for several hours, more than 95% of

each complex remained unreacted. That said, a very low

yield (i.e., several crystals) of the magnesium(II) iodide

ACTHNUTRGNEUNG

complex [(^MesNacnac)Mg(m-I)₂(^MesNacnac)] deposited in the

tube upon cooling, although there was no spectroscopic or

other evidence for the corresponding generation of

[(^MesNacnac)BeBe(^MesNacnac)].

The

complex

[(^MesNacnac)Mg(m-I)₂(^MesNacnac)] was crystallographically

AHCTUNGTERNNUNG

characterized although no spectroscopic data were ob-

tained.^[27]

Similarly,

[{(^DippNacnac)CaI

complex [{(^tBuNacnac)CaI

AHCTUNGTRENNUNG

attempts

(OEt₂)}₂] 14 or the previously reported

(thf)}₂]^[28a]with sodium or potassi-

were

made

to

reduce

AHCTUNGTRENNUNG

um in toluene. No evidence for the formation of calcium(I)

compounds was obtained, and the only product isolated

from the reductions of 14 was the known homoleptic com-

plex [Ca(^DippNacnac)₂],^[28b,c]whereas the sodium reduction of

this originates from

a mixed hydride/iodide complex,

[(^DippNacnac)Mg (m-I)Mg(^DippNacnac)] (also see com-

G

ACHTUNGTRENNUNG

plex 18), although the product could not be isolated. The

fact that significant amounts of hydride by-products are

formed in this reaction and apparently not the other two is

unusual. We cannot be sure why this is but it is noteworthy

that the precursor to 17 (i.e., 9) does not incorporate coordi-

nated ether, whereas the precursor to 2, [(^DippNacnac)MgI-

[{(^tBuNacnac)CaI

ACHTUNGTREN(GNUN thf)}₂] afforded a moderate yield (ca.

50%) of the crystallographically and spectroscopically char-

acterized complex [{Na(^tBuNacnac)}₂] (20). These results sug-

gest that because of the larger size of calcium relative to

magnesium, b-diketiminate coordinated calcium(I) dimers

may not be stable towards disproportionation and/or other

decomposition processes at room temperature.^[29]

ACHTUNGTRENNUNG(OEt₂)], does. If the reduction that gave 2 is accompanied

by hydrogen abstraction from diethyl ether (to give 3) but

not from toluene, this might explain why the reaction mix-

ture that generates 17 is free of magnesium hydride by-prod-

ucts. It could then be argued that the reduction that gives 16

from an ether-coordinated precursor does generate magnesi-

um hydride by-products, but that these by-products are un-

stable with respect to redistribution to give the observed

complex 19 and insoluble magnesium hydride materials such

as MgH₂or MgHI. It is unlikely that 19 forms through the

disproportionation of 16 because the latter compound is

thermally robust and its toluene solutions show no signs of

decomposition for at least several weeks at room tempera-

ture.

All of the compounds 15–20 were spectroscopically char-

acterized, although comment will be passed here only on

the data for 16–18. The ¹H NMR spectrum of 16 is indicative

of this compound possessing high symmetry in solution in

that it displays three sharp methyl resonances (two associat-

ed with the mesityl groups and one arising from the back-

bone methyl substituents). This implies unrestricted partial

ꢀ

or full rotation of its mesityl groups about the exocyclic N

C bonds and/or rotation of the two magnesium heterocycles

ꢀ

about the Mg Mg bond of the compound. Similarly, the

spectrum of 17 exhibits only two isopropyl methyl doublet

resonances and one methine septet resonance. However, at

298 K these are broad, which indicates restricted rotation of

its 2,6-diisopropylphenyl groups and/or the two sterically

bulky magnesium heterocycles. Heating solutions of 17 in

[D₆]benzene to 340 K leads to a sharpening of all resonances

in the spectrum. This implies that at this temperature the

previously restricted rotations become rapid with respect to

the NMR timescale. No signals were observed in the

²⁵Mg{¹H} NMR spectra of nearly saturated [D₆]benzene sol-

utions of either 2, 16, or 17, presumably because of the

quadrupolar nature and low natural abundance (I=5/2,

In attempts to extend the above-mentioned chemistry to

ꢀ

the formation of a Be Be bonded dimer, the beryllium(II)

iodide complex 13 was reduced with either lithium in diethyl

ether, sodium in toluene, or potassium in a diethyl ether/tol-

1

uene (1:40) mixture. In all cases, the H NMR spectra of the

reaction mixtures revealed that numerous products had

been formed, none of which could be identified. It is possi-

ble that because of the smaller size of beryllium relative to

magnesium, the reduction of 13 initially yields the radical

[(^MesNacnac)Be ], which undergoes intramolecular reactions

10% abundant) of that nucleus. The H NMR spectrum of

1

C

(e.g., C H activations) more rapidly than it can dimerize to

18 highlights sets of resonances for both its ^DippNacnac and

^MesNacnac ligands in addition to a singlet at d=3.92 ppm,

which corresponds to the bridging hydride ligand.

ꢀ

give [(^MesNacnac)BeBe(^MesNacnac)].^[26]It is of note that in

the first minute of the lithium reduction, the reaction solu-

tion took on a deep-blue color, which rapidly faded there-

after. This is perhaps indicative of the presence of a reactive

intermediate radical species, similar to that proposed. Given

the greater electronegativity of magnesium over beryllium,

the reduction of 13 with half an equivalent of

[(^MesNacnac)MgMg(^MesNacnac)] 16 in [D₆]benzene was also

Molecular ion peak envelopes having the expected isotop-

ic mass distributions were observed in the electron ioniza-

tion mass spectra (EIMS) of 16 and 17 (as was the case for

2), whereas the only identifiable fragments in the EIMS of

18 were derived from the free b-diketiminate ligands. The

infra-red (IR) spectra of 16 and 17 appear to show only

Chem. Eur. J. 2010, 16, 938 – 955

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943

C. Jones, A. Stasch et al.

ꢀ

ligand vibrational modes, and no Mg H stretching bands

could be assigned in the IR spectrum of 18. It is believed

that the latter are masked by ligand modes in the fingerprint

region of the spectrum. A number of low-wavenumber ab-

sorptions were observed in the Raman spectra of 16 and 17,

which could not be confidently assigned as arising from

ꢀ

Mg Mg stretching modes. It is noteworthy, however, that

the most intense of these (16: n˜ =151 cm^ꢀ1; 17: n˜ =154 cm^ꢀ1)

occur close to that for 2 (n˜ =148 cm^ꢀ1),^[10]and all are at

lower wavenumbers than that experimentally detected for

ꢀ

the Mg Mg vibration mode of the two-coordinate com-

pound ClMgMgCl (n˜ =176 cm^ꢀ1).^[3a]

Complexes 15–20 were crystallographically authenticat-

ed,^[27]although only the molecular structures of 16–18 are

depicted in Figure 2 (see Table 2 for the relevant metrical

ꢀ

parameters). Both 16 and 17 are Mg Mg bonded dimers but

there are significant differences between them. First, the

ꢀ

Mg Mg distance for the less-hindered compound 16

(2.808(1) ꢁ) is markedly shorter than that for the very-hin-

ꢀ

dered compound 17 (2.847(2) ꢁ). Interestingly, the Mg Mg

bond length in one polymorph of the previously reported

compound 2 (2.8457(8) ꢁ)^[10]is not significantly different to

that of 17, and in another polymorph it is slightly longer

(2.8624(15) ꢁ)^[14]despite the lesser steric buttressing of the

magnesium heterocycles of that compound. Although the ni-

trogen substituents of both complexes are the same, the

steric differences between the two compounds arise from

the variation in size of the backbone methyl (in 2) versus

tert-butyl substituents (in 17) of the compounds. This dispar-

ity can be quantified to some extent by an examination of

their C-N-C angles, which for 2 (mean=118.68) are consid-

erably less than those for 17 (mean=123.58).^[30]Differences

in ligand sterics can also be used to explain the fact that the

magnesium heterocycles of 16 are essentially planar, where-

as those of both 2 and 17 are somewhat distorted from

planar (mean distance of Mg atoms from the NCCCN least-

squares planes: 16=0.129 ꢁ, 2=0.529 ꢁ, 17=0.624 ꢁ).^[31]

Also of note is the fact that the dihedral angles between the

least-squares planes of the bulkier heterocycles of 2 and 17

(80.28 and 76.58, respectively) are much larger than that of

16 (43.98). The more obtuse angles of the former pair proba-

bly aid a minimization of the intramolecular interactions of

the bulky Dipp substituents of those compounds. It might be

expected that close to orthogonal heterocycles would also

be favored for 16. The fact that this does not occur may be

a result of crystal-packing effects overriding the intracyclic

interactions between the mesityl groups in the compound

Figure 2. Thermal ellipsoid (25%) drawings of 16–18. Hydrogen atoms

(except H(1) in the structure of 18) are omitted for clarity. Selected met-

rical parameters for these compounds are given in Table 2. Symmetry

transformations (’) for 16: ꢀx+1/2, y, ꢀz+1/2; 17: ꢀx+1, y, ꢀz+1/2.

ꢀ

and/or the likely weak barrier to rotation about its Mg Mg

bond. Whatever the case, it is worthy to mention that the

corresponding zinc(I) dimer [(^MesNacnac)ZnZn(^MesNacnac)]

(dihedral angle between least squares heterocycle planes=

ꢀ

44.68; Zn Zn distance=2.3813(8) ꢁ) is isostructural to

16.^[9d]

study was undertaken on 16, full details of which can be

found in the Supporting Information.^[27]All hydrogen and

non-hydrogen atoms of the molecule were included in the

refinement. The observed metrical parameters for the com-

pound are essentially the same as those obtained from the

Although the absence of hydride ligands bridging the Mg

centers of 2 has been proven by the preparation of the mag-

nesium(II) hydride complex 3 (see above), this is not yet the

case for 16 (see below). Accordingly, a neutron diffraction

944

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Chem. Eur. J. 2010, 16, 938 – 955

Stabilized Mg^IDimers and Mg^IIHydride Complexes

FULL PAPER

Table 2. Selected interatomic distances [ꢁ] and angles [8] for 16–18.

16

17

18

ꢀ

Mg1 N1

2.039(1)

2.037(2)

2.808(1)

1.329(2)

1.331(2)

1.407(2)

1.405(2)

91.99(6)

135.08(5)

132.86(5)

Mg1 N1

2.077(2)

2.069(2)

2.847(2)

1.324(3)

1.350(3)

1.429(3)

1.401(3)

93.90(9)

133.35(7)

132.12(7)

Mg1 N1

2.036(4)

1.88(8)

1.410(8)

2.028(5)

1.326(8)

1.411(9)

Mg1-N2

N1-C2

C3-C4

Mg2-H1

N4-C33

Mg1···Mg2

2.037(5)

1.316(7)

1.400(8)

1.98(8)

1.325(8)

3.101(2)

Mg1 I1

2.865(2)

1.345(7)

2.024(5)

2.758(2)

1.401(9)

ꢀ

Mg1 N2

Mg1 H1

N2 C4

ꢀ

Mg1 Mg1

Mg1 Mg1’

C2 C3

Mg2 N4

ꢀ

N1 C2

Mg2 N3

Mg2 I1

ꢀ

N2 C4

N3 C31

C31 C32

ꢀ

C2 C3

C32 C33

ꢀ

C3 C4

N2-Mg1-N1

N1-Mg1-N2

Mg2-I1-Mg1

93.6(2)

66.92(6)

N4-Mg2-N3

Mg2-H1-Mg1

94.6(2)

107(1)

N2-Mg1-Mg1’

N1-Mg1-Mg1’

N2-Mg1-Mg1’

N1-Mg1-Mg1’

X-ray crystal structure. Importantly, no significant residual

either THF or DMAP, which led to moderate isolated yields

of the adduct complexes

[(^MesNacnac)Mg(L)-

ACHTUNGTRENNUNG

Mg(L)(^MesNacnac)], in which L=THF (21) or DMAP (22)

as described in [Eq. (9)]. In contrast, the more bulky magne-

sium(I) dimer 17 does not react when dissolved in neat THF

ꢀ

nuclear density was located near the Mg Mg vector of the

compound. Therefore, the possibility of hydride ligands be-

tween the magnesium centers of the compound can be elim-

inated.

The molecular structure of 18 reveals it to possess two es-

sentially co-planar magnesium heterocycles, which are bridg-

ed by one hydride and one iodide ligand. The hydride (H1)

was located from difference maps and its positional parame-

ters were freely refined. This allowed the observation that

the hydride and iodide ligands do not symmetrically bridge

the two magnesium centers, because the iodide has a signifi-

cantly closer interaction with the [Mg(^MesNacnac)] heterocy-

cle than the [Mg(^DippNacnac)] heterocycle. Conversely, the

hydride is more closely associated with the {Mg(^DippNacnac)}

fragment. The Mg···Mg separation (3.101(2) ꢁ) is signifi-

cantly longer than in the magnesium(I) compounds 2, 16, or

17 and in the magnesium(II) hydride dimer 3 (2.890(2) ꢁ).

and is recovered in good yield after its treatment with

DMAP in toluene or [D₆]benzene.^[32]Presumably, the low

reactivity of 17 towards Lewis base coordination is derived

from its sterically well-shielded Mg centers. It is interesting

that, although compound 21 readily loses its THF of coordi-

nation (at>858C under N₂), it is more resistant to this pro-

Reactivity of magnesium(I) dimers: The availability of a

series of magnesium(I) dimers of varying steric bulk,

namely, 17>2>16, presented the opportunity of comparing

the further reactivity of these compounds. In the first in-

stance, two magnesium heterocycle scrambling reactions

were attempted by dissolving approximately equimolar mix-

tures of 2 and 16 or 2 and 17 in [D₆]benzene and monitoring

cess than is

4

(L=THF. THF loss occurs at

>708C under N₂).^[13]It is thought that this higher stability

results from the lesser steric bulk of the b-diketiminate li-

gands of 21, which leads to stronger THF coordination than

in 4 (in which L=THF).

1

the solutions by H NMR spectroscopy. In each case no re-

Compounds 21 and 22 were spectroscopically character-

ized. As was the case for 4, the NMR spectra of 21 and 22

that were recorded in [D₆]benzene display fewer resonances

than would be expected if their THF or DMAP ligands re-

mained strongly coordinated in solution. It seems, therefore,

that a fluxional ligand dissociation/coordination process is

occurring for the complexes, which is rapid compared with

the NMR timescale, and leads to time-averaged structures

for the complexes that are more symmetrical than the solid-

state structures. The low solubility of complexes 21 and 22

in [D₈]toluene at temperatures below 08C precluded low-

temperature NMR spectroscopic studies on the compounds.

Although X-ray crystal structures of both 21 and 22 were

obtained, only that of 22 was of sufficient quality for inclu-

sion here (Figure 4, Table 3).^[33]The two Mg centers of the

compound possess flattened tetrahedral geometries with

action occurred at 258C or when the solutions were heated

at 1008C for one hour. This strongly suggests that there is

no appreciable dimer/monomer equilibrium in solution for

all of the compounds, despite the aforementioned experi-

ꢀ

mental evidence for the deformability of the Mg Mg bond

of 2. This result is, however, consistent with the relatively

ꢀ

high Mg Mg bond-dissociation energies that have been cal-

culated for magnesium(I) dimers.^[3a,6,13]

Compound 2 has been shown to readily form adducts 4

with several ether or pyridine Lewis bases (such as THF, di-

oxane, 4-tert-butylpyridine, or DMAP).^[13]X-ray crystallog-

raphy revealed the two magnesium heterocycles of all of

these complexes to be effectively parallel, as opposed to the

nearly orthogonal heterocycles in 2. This change in the ori-

entation of the heterocycles likely occurs to sterically ac-

commodate coordination of the Lewis bases. For compari-

son, the less bulky magnesium(I) dimer 16 was treated with

ꢀ

Mg N_DMAPbonds that are significantly longer than the Mg

N_Nacnacinteractions. Note that the former are somewhat

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945

C. Jones, A. Stasch et al.

Table 3. Selected interatomic distances [ꢁ] and angles [8] for 22 and 27–29.

22 27

28

29

ꢀ

Mg1 Mg2

2.937(1)

2.120(2)

2.126(2)

2.202(2)

2.131(2)

2.122(2)

2.209(2)

87.96(7)

111.49(5)

88.60(6)

111.84(5)

Mg1 N1

2.041(2)

2.072(2)

2.078(2)

2.042(2)

1.304(3)

1.312(3)

1.419(4)

97.95(8)

116.6(1)

118.0(2)

114.9(2)

Mg1 N1

2.020(3)

2.030(2)

2.051(2)

2.044(2)

1.303(3)

1.309(3)

1.423(4)

94.4(1)

Mg1 N1

2.060(1)

2.051(1)

2.062(1)

2.101(1)

2.011(1)

2.017(1)

1.952(1)

1.963(1)

1.302(2)

1.300(2)

1.282(2)

1.287(2)

1.548(2)

92.27(5)

94.19(5)

ꢀ

Mg1 N1

Mg1 N2

ꢀ

Mg1 N2

Mg1 N3

ꢀ

Mg1 N5

Mg1 N5’

Mg1 N4

ꢀ

Mg2 N3

N3 N4

Mg2 N5

ꢀ

Mg2 N4

N4 N5

Mg2 N6

ꢀ

Mg2 N7

N5 N5’

Mg2 O1

ꢀ

N2-Mg1-N1

N5-Mg1-Mg2

N3-Mg2-N4

N7-Mg2-Mg1

N2-Mg1-N1

Mg1-N3-N4

N3-N4-N5

N4-N5-N5’

N2-Mg1-N1

Mg1-N3-N4

N3-N4-N5

N4-N5-N5’

Mg2 O2

ꢀ

117.3(2)

114.4(2)

C24 N3

ꢀ

C25 N4

ꢀ

C24 O1

ꢀ

C25 O2

ꢀ

C24 C25

N1-Mg1-N2

N5-Mg2-N6

ꢀ

shorter than the related bonds in 4 (L=DMAP; Mg

N

_DMAP=2.235(2) ꢁ),^[13]which is consistent with the less-hin-

dered magnesium centers of 22. There are a number of

other notable differences between the geometries of the two

compounds. These include the dihedral angle between their

Mg heterocycle least-squares planes, which is much more

obtuse in 22 (72.28 as compared with 43.98 in 16) than in 4

(L=DMAP; 3.48 as compared with 80.28 in 2). In addition,

ꢀ

the Mg Mg distance in 22 (2.9369(12) ꢁ) is shorter than

that recorded for 4 (L=DMAP, 3.1962(14) ꢁ). However, it

should be pointed out that the latter compound co-crystal-

lized with approximately 8% of the corresponding magne-

sium(II) hydroxide complex [{(^DippNacnac)Mg

ACTHNUTRGENNU(G DMAP)ACHTUNGTERN(NUGN m-

OH)}₂],^[34]and therefore its Mg Mg distance cannot be con-

sidered as completely accurate. No similar co-crystallization

occurred for 22, and accordingly the magnitude of the signif-

ꢀ

icant increase (by ca. 0.13 ꢁ) in the Mg Mg distance of 16

upon coordination with DMAP (to give 22) is reliable. It is

very likely that the steric differences between the b-diketi-

minate ligands ^MesNacnac and ^DippNacnac are the origin of

the contrasting geometries of 22 and 4 (L=DMAP).

Figure 3. Previously reported reduction products from reactions of 2 with

unsaturated substrates.

It has been demonstrated that the magnesium(I) dimer 2

acts as a facile two-center/two-electron reducing agent to-

wards a variety of N- or O-functionalized unsaturated or-

ganic substrates. For example, its reactions with CyN=C=

NCy (Cy=cyclohexyl), PhN=NPh, AdN₃(Ad=1-adaman-

tyl), or tBuN=C=O gave good yields of the complexes 23–

26, respectively (Figure 3).^[15]The mechanisms of these reac-

tions are thought to involve coordination of each substrate

at the magnesium centers of 2 prior to their reduction.^[35,36]

Evidence for this includes the fact that compound 4 (L=

THF) is unreactive towards CyN=C=NCy in neat THF,

most likely because its magnesium centers are coordinative-

ly saturated. If this proposal is correct, it was believed that

the more accessible Mg centers of 16 would lead to it being

a more effective reducing agent than 2, whereas the hin-

dered system 17 would be a less effective reductant.

a reaction between 17 and the less-hindered substrate

tBuN=C=O at room temperature although an inseparable

mixture of products resulted from this. Compound 17 be-

haved similarly to 2 with regard to its reaction with AdN₃,

which proceeded at ꢀ788C and afforded a moderate yield

of the azide coupled product 27 as described by [Eq. (10)].

Reactions of less-hindered 16 with all four substrates took

place rapidly in toluene at ꢀ788C, but tractable products

from those with the carbodiimide or azobenzene could not

This proved to be the case because the more hindered of

the four substrates, CyN=C=NCy and PhN=NPh, did not

react with 17 in toluene at ambient temperature. There was

946

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Chem. Eur. J. 2010, 16, 938 – 955

Stabilized Mg^IDimers and Mg^IIHydride Complexes

FULL PAPER

be isolated upon work-up.^[37]The reaction with the azide

yielded a product analogous to 25 and 27 (namely, complex

28), whereas that with tBuN=C=O afforded a moderate iso-

lated yield of the reductively coupled product 29 as de-

scribed by [Eq. (11)]. The structural similarities between the

It would be expected that the addition of dihydrogen to

ꢀ

the Mg Mg bonds of magnesium(I) dimers to give com-

pounds of the type [LMg

A

mic process. Indeed, for a range of complexes in which L is

an N,N’-chelating guanidinate ligand (such as 1), calculations

have shown the magnitude of this exothermicity to be ap-

proximately 24 kcalmol^ꢀ1.^[41]This can be compared with the

enthalpy of hydrogenation of magnesium metal to give

MgH_2(s), which is ꢀ17.9 kcalmol^ꢀ1.^[42]Despite this, high tem-

peratures (>2508C) and/or H₂pressures are generally re-

quired to overcome the kinetic barrier to this reaction. Simi-

larly, compounds 1 and 2 have been found to be unreactive

towards H₂at one atmosphere pressure and 808C in arene

solvents.^[10]In the current study we have extended this prior

work to the treatment of the less-hindered dimer 16 with di-

hydrogen. Under one atmosphere of H₂in toluene, the com-

pound showed no signs of hydrogenation after 4 h at 808C.

When higher hydrogen pressures were employed in reaction

vessels containing toluene solutions of either 16 or 2 (ca.

5 atm.), and the mixtures were heated at 808C for four

hours, still no hydrogenation reactions occurred and the

starting materials were recovered. When the pressures in

these reaction vessels were increased to approximately

70 atmospheres and the mixtures were heated at 808C for

four hours, NMR spectroscopic analyses showed that the re-

actions yielded numerous products, which are believed to be

b-diketiminate cleavage and/or hydrogenation products. On

no occasion was there any convincing evidence for the pres-

ence of the target magnesium hydride complexes in the re-

action mixtures.

azide-coupled products 25, 27, and 28 are obvious, and all

are isostructural to the only other known alkyl azide-cou-

ACTHNUTRGNEUNG

pled complexes [(L)Fe^II(m-AdN₆Ad)Fe^II(L)] (L=^DippNacnac

or ^tBuNacnac) reported by Holland and co-workers to be

formed in reactions of AdN₃with b-diketiminato iron(I)

complexes.^[38]Like the iron complexes, compounds 25, 27,

and 28 do not appear to be shock or thermally sensitive to

detonation, despite containing covalently bonded N₆chains

within their dianionic bridging ligands. This contrasts to

some related hexaazadienes, RNNN(R)N(R)NNR (R=

alkyl, aryl etc.,), which are high-energy materials that can

be susceptible to explosion.^[39]Metal-induced isocyanate re-

ductive-coupling reactions have been previously reported,

but their products normally incorporate a bridging N,O-che-

lating ligand, for example, [L_nM{ON(R)C₂N(R)O}ML_n],

with two delocalized OCN fragments.^[40]Conversely, the

coupled ligand in 26 was reported to be largely localized

and exhibited an unprecedented N,O/O,O’-ligation of its two

Mg centers. In 29, the same bridging ligand exhibits delocali-

zation over its NCO units, but coordinates the two

{Mg(^MesNacnac)} fragments in a N,N’/O,O’-mode. To the

best of our knowledge this has not been previously observed

in an isocyanate coupled complex. The differences between

the ligating mode of [O₂C₂N₂tBu₂]^2ꢀin 26 and 29 are again

thought to be of a steric origin. That is, N,N’-chelation of

the {Mg(^DippNacnac)} fragment by two bulky NtBu units is

expected to be disfavored, as compared with a similar chela-

tion of the smaller {Mg(^MesNacnac)} moiety.

Preparation and characterization of magnesium(II) hydride

complexes: As already mentioned, definitive proof of the

absence of hydride ligands bridging the metal centers of 2

came with the synthesis of 3. This compound was prepared

in moderate yield by heating

a hexane solution of

[(^DippNacnac)MgnBu] and PhSiH₃at reflux for two days.^[13,43]

Its subsequent treatment with THF led to the adduct

[(^DippNacnac)Mg

G

N

(thf)(^DippNacnac)].^[13]

Com-

ACHTUNGTRENNUNG

H)₂MgL],^[44,45]and it was shown to act as an effective hydro-

magnesiation reagent towards a range of unsaturated sub-

strates.^[15]To extend the chemistry of well-defined, neutral

magnesium hydride complexes, and to draw comparisons

with the magnesium(I) dimers 16 and 17, the preparation of

magnesium hydride complexes incorporating the ^MesNacnac

and ^tBuNacnac ligands was explored.

The spectroscopic data for 27–29 are consistent with them

retaining their solid-state structures in solution and will not

be commented on here. Each compound was crystallograph-

ically authenticated and their molecular structures are

shown in Figure 4 (see Table 3). The structures of 27 and 28

are closely related to each other and that of 25 in that they

possess distorted tetrahedral Mg centers that are chelated

by close to planar [AdN₆Ad]^2ꢀligands. The bond lengths of

the N₆fragment of each compound are suggestive of deloc-

In an attempt to access the magnesium hydride complex

ACTHNUTRGNEUNG

[(^MesNacnac)Mg(m-H)₂Mg(^MesNacnac)], ^MesNacnacH was

heated with one equivalent of MgnBu₂in toluene for two

hours at 608C and the volatiles were removed in vacuo to

yield a solid residue. This was dissolved in hexane, treated

with PhSiH₃, and the solution was heated at reflux for three

days. The only identifiable product obtained from the reac-

tion mixture was a low isolated yield of the homoleptic com-

ꢀ

alization over the outer N₃units, whereas the central N N

distance is reminiscent of

a

single bond. In 29, the

ꢀ

MgO₂C₂N₂Mg bicyclic unit is effectively planar and its C O

ꢀ

and C N distances are normal for delocalized double bonds,

ꢀ

whereas the central C C separation is indicative of a single

bond.

pound 19. This result could indicate that [(^MesNacnac)Mg

ACHTUNGTRENNUNG

Chem. Eur. J. 2010, 16, 938 – 955

ꢀ 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

www.chemeurj.org

947

C. Jones, A. Stasch et al.

Figure 4. Thermal ellipsoid (25%) drawings of 22 and 27–29. Hydrogen atoms from all structures and isopropyl groups from the structure of 27 are omit-

ted for clarity. Only one of the two crystallographically independent molecules of 28 is shown. Selected metrical parameters for these compounds are

given in Table 3. Symmetry transformations (’) for 27: ꢀx, ꢀy+2, ꢀz; 28: ꢀx+1, ꢀy, ꢀz.

H)₂Mg(^MesNacnac)] was generated in the reaction, but the

compound is unstable with respect to redistribution under

the reaction conditions employed. Compound 19 was subse-

quently intentionally synthesized in good yield (68%) by

the reaction of two equivalents of ^MesNacnacH with

MgnBu₂.^[46]All other attempts to prepare [(^MesNacnac)Mg-

in [Eq. (12)]. It is of note that a higher reaction temperature

is required for the synthesis of 30 than for the preparation

of 3, probably because of the greater steric bulk of the b-di-

ACHTUNGTRENNUNG

(m-H)₂Mg(^MesNacnac)] such as by the treatment of

[(^MesNacnac)MgCH₂Ph] with PhSiH₃have so far proved to

be fruitless.

It seemed reasonable that magnesium hydride complexes

incorporating the bulkier ^tBuNacnac ligand would be more

ACTHNUTRGNEUNG

accessible than [(^MesNacnac)Mg(m-H)₂Mg(^MesNacnac)]. An

example of such a complex was ultimately prepared by de-

protonating ^tBuNacnacH with MgnBu₂to yield in situ gener-

ated [(^tBuNacnac)MgnBu], which was subsequently treated

with PhSiH₃and heated at reflux in toluene for two days.

Upon work-up of the reaction mixture, the complex

ketiminate ligand in the former. Unlike 3, compound 30

does not appear to form an isolable complex with THF, but

when treated with the stronger Lewis base, DMAP, a good

yield of the monomeric magnesium hydride complex

[(^tBuNacnac)Mg(H)

ACTHNUTRGNE(NUG DMAP)] (31) resulted as shown in

[(^tBuNacnac)Mg

G

[Eq. (13)]. This represents the first example of a complex

that is structurally authenticated as possessing a terminal

colorless crystalline material in moderate yield as described

948

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ꢀ 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Chem. Eur. J. 2010, 16, 938 – 955

Stabilized Mg^IDimers and Mg^IIHydride Complexes

FULL PAPER

ꢀ

Mg H bond and it contrasts with the dimeric structure of

the

[(^DippNacnac)Mg

ACTHNGUTERNU(NG thf)ACHTUNGTERN(NUNG m-H)₂Mg-

ACHTUNGTRENNUNG

ble with their solid-state structures (see below) and both ex-

hibit singlet hydride resonances (30: d=3.83 ppm, 31: d=

1

4.65 ppm) in their H NMR spectra that lie close to those re-

ported for 3 (d=4.03 ppm) and [(^DippNacnac)Mg

N

ACHTUNGERTN(NUNG m-

H)₂MgACHTUNGTRENNUNG

of the IR spectra (Nujol mulls) of solid samples of both

ꢀ

complexes, Mg H stretching bands could not be confidently

assigned. In the case of 30, this is not surprising because

stretching bands associated with Mg-H-Mg moieties have

been reported to occur in the range 1250–1300 cm^ꢀ1, and

thus for 30 these could be masked by ligand vibration

modes.^[44]The terminal Mg H stretching absorption of 31

ꢀ

would, however, be expected to occur at a significantly

higher wavenumber. For amido magnesium hydride com-

plexes, [{MgACHTUNGTRENNUNG(NR₂)H}₂], purported to exhibit bridging amide

ꢀ

and terminal hydride ligands, Mg H stretching bands in the

range 1580–1630 cm^ꢀ1have been reported.^[44]The IR spec-

trum of 31 exhibits an intense band centered at 1614 cm^ꢀ1,

ꢀ

which was originally considered to arise from a Mg H

stretching mode. However, an examination of the IR spec-

trum of the isostructural complex 12 showed it to be almost

identical to that of 31, and therefore, this band likely results

Figure 5. Thermal ellipsoid (25%) drawings of 30 and 31. Hydrogen

atoms are omitted for clarity. Selected metrical parameters for these

compounds are given in Table 4.

ꢀ

from a stretching mode associated with an unsaturated N C

bond of the DMAP ligand. Preparation of the deuterated

analogues of 30 and 31 would shed light on the positions of

ꢀ

the Mg H stretching bands of these complexes. This would,

Table 4. Selected interatomic distances [ꢁ] and angles [8] for 30 and 31.

however, be very difficult to achieve by using the synthetic

methods employed to generate the nondeuterated com-

pounds, and thus was not attempted.

30

31

ꢀ

Mg1···Mg2

2.835(2)

2.053(4)

2.071(4)

1.91(5)

1.80(5)

2.056(4)

2.036(4)

1.82(5)

1.84(5)

94.5(2)

78(2)

Mg1 N1

2.066(3)

2.077(3)

2.135(3)

1.75(7)

94.4(1)

104.4(1)

105.7(1)

124(2)

ꢀ

Mg1 N1

Mg1 N2

Both 30 and 31 were crystallographically characterized

and their molecular structures are depicted in Figure 5 (see

Table 4). The hydride ligands of both complexes were locat-

ed from difference maps and their positional parameters

freely refined. In the case of 30, this highlights one magnesi-

um atom of the compound (Mg(1)) to have a distorted

square-planar geometry, whereas the other (Mg(2)) has dis-

torted tetrahedral geometry. Unusually, this results in the

two magnesium heterocycles of the compound being close

to orthogonal (the dihedral angle between least-squares

planes=77.88 in 30 as compared with 76.58 in 17), which

contrasts with the close to parallel magnesium heterocycles

in 3. These differences are almost certainly a result of the

differing steric profiles of the b-diketiminate ligands in the

complexes. That said, the Mg···Mg separation in 30

ꢀ

Mg1 N2

Mg1 N3

ꢀ

Mg1 H1

ꢀ

Mg1 H2

N2-Mg1-N1

N1-Mg1-N3

N2-Mg1-N3

N1-Mg1-H1

N2-Mg1-H1

N3-Mg1-H1

ꢀ

Mg2 N3

ꢀ

Mg2 N4

ꢀ

Mg2 H1

ꢀ

Mg2 H2

121(2)

106(2)

N1-Mg1-Mg2

H1-Mg1-H2

N3-Mg2-N4

H1-Mg2-H2

96.5(2)

80(2)

(2.835(2) ꢁ) is shorter than that in the less-hindered com-

ꢀ

pound 3 (2.890(2) ꢁ), and intriguingly, is less than the Mg

Mg bond length of the magnesium(I) dimer 17. Compound

Chem. Eur. J. 2010, 16, 938 – 955

ꢀ 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

www.chemeurj.org

949

C. Jones, A. Stasch et al.

31 is monomeric and possesses a distorted tetrahedral mag-

nesium center that contains a terminal hydride ligand. The

tively confirmed by a neutron diffraction study of that com-

plex.

ꢀ

Mg N_Nacnacand Mg N_DMAPbond lengths are significantly

less than those in the magnesium(I) dimer 4 (L=DMAP),

but are close to those in the isostructural magnesium(II)

iodide complex 12.

Experimental Section

General methods: All manipulations were carried out by using standard

Schlenk and glove-box techniques under an atmosphere of high-purity di-

nitrogen. Toluene, hexane, THF, and benzene were distilled over molten

potassium, whereas diethyl ether was distilled over a Na/K alloy (25:75).

¹H and ¹³C{¹H} NMR spectra were recorded on either Bruker DPX 300

or DPX 400 spectrometers in deuterated solvents and were referenced to

Conclusion

In summary, the preparation and characterization of a series

of magnesium(II) iodide complexes incorporating b-diketi-

minate ligands of varying steric bulk and denticity has been

described. In addition, one example each of a b-diketimina-

to beryllium iodide and calcium iodide complex has been

synthesized and fully characterized. The reductions of all

metal(II) iodide complexes by using various reagents were

attempted. In two instances, previously unreported dimeric

magnesium(I) complexes 16 and 17 resulted from the reduc-

tion reactions. It is apparent from the other reactions that

the less bulky magnesium(I) dimer [(^PhNacnac)MgMg-

1

the residual H or ¹³C resonances of the solvent used. In data assignments

m_cdenotes the chemical shift at the center of a multiplet. Mass spectra

were obtained from the EPSRC National Mass Spectrometric Service at

Swansea University. IR spectra were recorded by using a Perkin–Elmer

RXI FTIR spectrometer as Nujol mulls between NaCl plates. Raman

spectra were recorded for crystalline samples sealed in glass capillaries

under dinitrogen by using a Renishaw RM2000 microRaman spectrome-

ter with 782 nm excitation from a diode laser. Melting points were deter-

mined in sealed glass capillaries under dinitrogen and are uncorrected.

Microanalyses were obtained from Campbell Microanalytical (Ottago,

NZ). ^DippNacnacH,^{[48] Ph}NacnacH,^{[49] Mes}NacnacH,^{[48] Dmeda}NacnacH^[50], and

^tBuNacnacH^[51]were synthesized by variations of literature procedures. All

other reagents were used as received.

ACHTUNGTRENNUNG

(^PhNacnac)] is unstable with respect to disproportionation,

[(^DippNacnac)MgI

ACTHNUGTRENNG(U OEt₂)] (5): A freshly prepared solution of MeMgI

and that the potentially tridentate b-diketiminate ligand

^DmedaNacnac is not effective for the synthesis of isolable

magnesium(I) complexes. The attempted reductions of ber-

yllium(II) and calcium(II) iodide precursor complexes have

not been successful so far, which indicates that b-diketimi-

nate stabilized beryllium(I) and calcium(I) complexes may

be difficult targets to achieve.

(25.4 mmol) in diethyl ether (80 mL) was added over 20 min to a stirred

solution of ^DippNacnacH (9.50 g, 22.7 mmol) in diethyl ether (100 mL) at

ꢀ208C, yielding a colorless precipitate. The suspension was warmed to

room temperature and stirred for 1 h after which time the precipitate of

5 was collected by filtration. The supernatant solution was concentrated

to ca. 40 mL and cooled to ꢀ308C to afford a second crop of 5 (yield=

11.0 g, 75%). The spectroscopic data for the complex were identical to

those previously reported.^[18]

A comparison of the reactivity of 16, 17, and the previous-

ly reported magnesium(I) complex 2 towards a variety of

Lewis bases and unsaturated organic substrates has been

carried out. The results of these investigations show the

complexes to be facile two-center/two-electron reductants,

and imply that their steric bulk is inversely proportional to

their reactivity towards the substrates studied. The tunable

and often selective reducing abilities of these compounds,

coupled with their solubility, ease of handling, and straight-

forward syntheses give them much potential as alternatives

to more classical reducing agents such as s-block metals or

Sm^IIcompounds,^[47]which are widely employed in organic

and organometallic synthetic methodologies.

ACHUTNRGENNUG ACHUTNGTREN(NUGN OEt₂)] (6): The compound was synthesized by using a

[(^PhNacnac)MgI

similar procedure to that employed for the preparation of 5, but by using

^PhNacnacH (2.5 g, 10.0 mmol). After work-up compound 6 was obtained

as

a yellow crystalline solid (yield=2.90 g, 61%). M.p. 102–1078C;

¹H NMR (300 MHz, 298 K, C₆D₆): d=0.54 (t, ³J_HꢀH=7.0 Hz, 6H;

CH₂CH₃), 1.73 (s, 6H, NCCH₃), 3.26 (q, ³J_HꢀH=7.0 Hz, 4H; CH₂CH₃),

4.75 (s, 1H, CH), 6.61–7.39 ppm (m, 10H; Ar-H); ¹³C{¹H} NMR:

(75.5 MHz, 298 K, C₆D₆): d=13.5 (CH₂CH₃), 23.7 (NCCH₃), 65.9

(CH₂CH₃), 97.2 (CH), 124.3 (Ar-C), 125.4 (Ar-C), 129.3 (Ar-C), 149.9

(Ar-C), 168.0 ppm (NCCH₃); IR (Nujol): n˜ =1632 (w), 1595 (m), 1552

(s), 1523 (s), 1485 (s), 1298 (m), 1315 (m), 1279 (m), 1194 (m), 1123 (m),

1090 (m), 1073 (m), 1029 (s), 997 (m), 764 (m), 753 (m), 700 cm^ꢀ1(m).

[(^MesNacnac)MgI

ACTHNUGTRENNG(U OEt₂)] (7): The compound was synthesized by using a

similar procedure to that employed for the preparation of 5, but by using

^MesNacnacH (10.0 g, 29.9 mmol). After work-up compound 7 was ob-

tained as a colorless crystalline solid (yield=14.60 g 68%). M.p. 192–

1948C; ¹H NMR (300 MHz, 298 K, C₆D₆): d=0.61 (brt, ³J_HꢀH=7.0 Hz,

6H; CH₂CH₃), 1.60 (s, 6H; NCCH₃), 2.19 (s, 12H; o-CH₃), 2.59 (brs, 6H;

p-CH₃), 3.18 (q, ³J_HꢀH=7.0 Hz, 4H; CH₂CH₃), 4.91 (s, 1H; CH),

6.80 ppm (s, 4H; Ar-H); ¹³C{¹H} NMR (75.5 MHz, 298 K, C₆D₆): d=15.5

(br; CH₂CH₃), 19.1 (br; o-CCH₃), 21.0 (p-CCH₃), 23.6 (NCCH₃), 66.0

(CH₂CH₃), 95.4 (CH), 129.0 (Ar-C), 130.2 (Ar-C), 133.6 (Ar-C), 144.1

(Ar-C), 169.2 ppm (NCCH₃); IR (Nujol): n˜ =1742 (w), 1624 (m), 1608

(m), 1553 (s), 1513 (s), 1259 (s), 1225 (s), 1192 (s), 1146 (s), 1089 (s), 1014

(s), 893 (m), 858 (s), 832 (m), 798 (m), 776 (m), 747 (m), 729 (m), 650

(w), 629 cm^ꢀ1(m); EIMS: m/z (%): 557.3 (2) [M⁺ꢀH], 334.3 (12)

To definitively disprove the presence of bridging hydride

ligands in 16 and 17, attempts were made to prepare their

magnesium(II) hydride counterparts [(^MesNacnac)Mg

ACHTUNGTRENNUNG

H)₂Mg(^MesNacnac)]

and

[(^tBuNacnac)Mg

ACHTUNGTRENNUNG

ACHTUNGTRENNUNG(

accessed in this study and it was found to have very differ-

ent properties to 17, thereby confirming that 17 is not a

magnesium hydride complex. Its treatment with the strong

Lewis base, DMAP, led to the formation of the monomeric

[

^MesNacnacH⁺]; elemental analysis calcd (%) for C₂₇H₃₉MgIN₂O (M_r=

complex, [(^tBuNacnac)Mg(H)

ACTHNUTRGNE(UNG DMAP)], which exhibits the

558.82): C 58.03, H 7.03, N 5.01; found: C 57.74, H 7.13, N 5.07.

[(^DmedaNacnac)MgI

(OEt₂)] (8): The compound was synthesized by using a

only known example of a structurally characterized terminal

AHCTUNGTRENNUNG

ꢀ

Mg H moiety. Although the other magnesium(II) hydride

similar procedure to that employed for the preparation of 5, but by using

^DmedaNacnacH (2.50 g, 7.70 mmol). After work-up compound 8 was ob-

tained as a colorless crystalline solid (yield=3.50 g, 81%). M.p. 145–

1508C; EIMS: m/z (%): 553.4 (10) [M⁺]; ¹H NMR (300 MHz, 298 K,

complex [(^MesNacnac)Mg

G

isolated, the absence of hydride ligands in 16 was alterna-

950

www.chemeurj.org

ꢀ 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Chem. Eur. J. 2010, 16, 938 – 955

Stabilized Mg^IDimers and Mg^IIHydride Complexes

FULL PAPER

C₆D₆): d=1.03 (t, ³J_HꢀH=6.9 Hz, 6H; CH₂CH₃), 1.15 (d, ³J_HꢀH=6.9 Hz,

690.3 (6) [(^MesNacnac)₂Mg⁺], 675.3 (4) [(^MesNacnac)₂Mg⁺ꢀMe], 557.3 (4)

[M⁺+H], 334.1 (92) [^MesNacnacH⁺]; elemental analysis calcd (%) for

C₂₇H₃₆MgIN₂O (M_r=555.80): C 58.24, H 6.70, N 5.03; found: C 58.17, H

6.84, N 4.96.

6H; CHACHTUNGTRENNUNG AHCTUNGTREN(NUGN CH₃)₂), 1.60 (s, 3H;

(CH₃)₂), 1.40 (d, ³J_HꢀH=6.9 Hz, 6H; CH

3

NCCH₃), 1.65 (s, 3H; NCCH₃), 1.90 (s, 6H; NCH₃), 2.21 (t, J_HꢀH

=

6.0 Hz, 2H; NCH₂CH₂N), 2.73 (t, ³J_HꢀH=6.0 Hz, 2H; NCH₂CH₂N), 3.22

(sep, ³J_HꢀH=6.9 Hz, 2H; CHMe₂), 3.33 (q, ³J_HꢀH=6.9 Hz, 4H; CH₂CH₃),

4.74 (s, 1H; NCCH), 7.17–7.14 ppm (m, 3H; Ar-H); ¹³C{¹H} NMR

(75.5 MHz, 298 K, C₆D₆): d=15.1 (CH₂CH₃), 21.8 (NCCH₃), 24.4 (CH-

[(^tBuNacnac)MgI

ACHTNUTRGNE(NUG DMAP)] (12): DMAP (32 mg, 0.26 mmol) was added at

208C to a solution of 9 (0.115 g, 0.23 mmol) in toluene (6 mL), affording

a colorless crystalline precipitate of 12. The precipitate was collected by

filtration, the supernatant was concentrated to ca. 3 mL and stored over-

night at 48C to yield a second crop of 12 (yield=0.11 g, 60%). M.p. slow

A

R

ACHTUGNTRNEN(UNG CH₃)₂), 43.9

A

ACHTUNGTRENNUNG

decomposition above ca. 2508C; ¹H NMR (300 MHz, 298 K, C₆D₆): d=

(CH₂CH₃), 95.6 (CH), 124.0 (Ar-C), 125.5 (Ar-C), 142.3 (Ar-C), 145.5

(Ar-C), 168.2 (NCCH₃), 169.0 ppm (NCCH₃); IR (Nujol): n˜ =1663 (w),

1624 (w), 1552 (m), 1524 (s), 1399 (m), 1379 (s), 1344 (s), 1315 (m), 1289

(w), 1255 (m), 1185 (w), 1148 (w), 1096 (w), 1043 (m), 1020 (m), 1000

(w), 895 (w), 840 (w), 787 cm^ꢀ1(m).

3

1.07 (d, ³J_HꢀH=6.9 Hz, 6H; CH

C

A

R

ACHTUNGTRENNUNG(CH₃)₂),

3

G

ACHTUNGTRENNUNG

3

[(^tBuNacnac)MgI] (9): MgnBu₂(1.0m solution in heptane, 3.28 mL,

3.28 mmol) was added to a solution of ^tBuNacnacH (1.60 g, 3.19 mmol) in

toluene (40 mL) at 208C. The mixture was heated to 1008C for 16 h. All

volatiles were removed in vacuo to give a colorless solid residue. This

was dissolved in toluene (30 mL) and a solution of iodine (0.849 g,

3.35 mmol) in toluene (20 mL) was added to it at ꢀ208C. An immediate

color change occurred, leaving a deep-yellow solution that was stirred for

3 h at room temperature. All volatiles were removed in vacuo, the resi-

due was extracted with hexane (50 mL), and the extract was cooled to

ꢀ308C giving colorless crystals of 9. Concentration of the supernatant to

ca. 20 mL and storing at ꢀ308C overnight yielded another crop of 9

(yield=1.25 g, 60%). M.p. 176–1788C; ¹H NMR (300 MHz, 298 K,

ACHTNUGTRNEN(UGN CH₃)₂), 5.61 (s, 1H; CH), 5.82 (brm_c, 2H; DMAP m-Ar-H), 6.97–7.11

(m, 6H; Ar-H), 8.59 ppm (brm_c, 2H: DMAP-o-Ar-H); ¹³C{¹H} NMR

(75.5 MHz, 298 K, C₆D₆): d=23.2, 24.1, 27.1, 28.4, 28.8, 29.1 (4ꢂCH-

ACHNUTRTGNE(UGN CH₃)₂, 2ꢂCHACHTUGNTERNN(GUN CH₃)₂), 33.2 (CACHNUTRGTEGNUN(N CH₃)₃), 38.1 (NAHCTUNGTRNEN(UNG CH₃)₂), 44.4 (CACHTUNGTRENNUNG(CH₃)₃),

95.9 (CH), 106.0 (DMAP m-Ar-C), 123.1 (Ar-C), 123.4 (Ar-C), 124.2

(Ar-C), 125.2 (Ar-C), 142.2 (Ar-C), 143.2 (Ar-C), 145.9 (Ar-C), 149.9

(DMAP p-Ar-C), 178.0 ppm (CCACHTUNRGTNEGNU(CH₃)₃); IR (Nujol): n˜ =1621 (s), 1543

(m), 1492 (m), 1364 (m), 1316 (m), 1261 (m), 1214 (m), 1154 (m), 1091

(s), 1012 (s), 802 (s), 757 cm^ꢀ1(m); EIMS: m/z (%): 652.2 (3) [M⁺

ꢀDMAP], 595.2 (8) [M⁺ꢀDMAPꢀC₄H₉], 244.4 (100) [tBuCNDipp⁺].

[(^MesNacnac)BeI] (13): A Schlenk tube fitted with a Youngꢃs tap was

charged with beryllium powder (0.18 g, ca. 20.0 mmol) and diethyl ether

(20 mL) and then cooled to ꢀ808C. I₂(1.86 g, 7.33 mmol) and a catalytic

amount of HgI₂(ca. 10 mg) was added and the reaction vessel sealed.

The mixture was then allowed to slowly warm to room temperature with

rapid stirring. The ensuing exothermic reaction was controlled by cooling

the reaction flask when necessary. After the most vigorous stage of the

reaction had ceased, the resultant slurry was stirred at room temperature

C₆D₆): d=1.16 (s, 18H; C

(CH₃)₂), 1.43 (d, ³J_HꢀH=6.8 Hz, 12H; CH

6.8 Hz, 4H; CH(CH₃)₂), 5.44 (s, 1H; CH), 7.00–7.10 ppm (m, 6H; ArH);

¹³C{¹H} NMR (75.5 MHz, 298 K, C₆D₆): d=23.3 (CH

(CH₃)₂), 26.0 (CH-

(CH₃)₂), 28.7 (CH(CH₃)₂), 32.9 (C(CH₃)₃), 44.2 (C(CH₃)₃), 95.6 (CH),

124.2 (Ar-C), 126.6 (Ar-C), 141.3 (Ar-C), 143.8 (Ar-C), 177.9 ppm (CC-

ACHTUNGTRENNUNG(CH₃)₃); IR (Nujol): n˜ =1621 (m), 1317 (m), 1261 (m), 1208 (m), 1155

(CH₃)₃)_,1.24 (d, ³J_HꢀH=6.8 Hz, 12H; CH-

ACHTUNGTERNNUNG

3

A

ACTHUGNNRETN(NUG CH₃)₂), 3.22 (sept, J_HꢀH=

ACHTUNGTRENNUNG

AHCTUNGTRENNUNG

A

E

N

ACHTUNGTRENNUNG

for 6 h yielding a grey precipitate of [BeI

cooled to 08C and a slurry of [K(^MesNacnac)] (5.53 mmol, prepared in

situ from the reaction of ^MesNacnacH with K[N

(SiMe₃)₂] in toluene) in

₂ACHTUGNTREN(UNGN OEt₂)₂]. This suspension was

(m), 1095 (s), 1054 (m), 1029 (m), 932 (m), 806 (m), 778 (m), 753 (m),

671 cm^ꢀ1(m); EIMS: m/z (%): 652.4 (35 [M⁺], 595.3 (46) [M⁺ꢀC₄H₉],

244.2 (100) [tBuCNDipp⁺]: EI accurate mass calcd for C₃₅H₅₃MgIN₂:

652.3098; found: 652.3098; elemental analysis calcd (%) for C₃₅H₅₃MgIN₂

(M_r=652.02): C 64.37, H 8.18, N 4.29; found: C 64.13, H 8.50, N 4.31.

AHCTUNGTRENNUNG

toluene (20 mL)/diethyl ether (10 mL) was added over 5 min. The resul-

tant suspension was stirred vigorously at 208C for one day. It was then

filtered and the residue was extracted with a mixture of toluene (15 mL)

and diethyl ether (10 mL). The combined extracts were concentrated to

ca. 12 mL and cooled to ꢀ308C to give colorless crystals of 13. Concen-

tration of the supernatant solution and cooling to ꢀ308C yielded a

second crop of the compound (yield=1.67 g, 66%). Data for isolated

[(^DippNacnac)MgI

ACHTUNGTRENNUNG(thf)] (10): Compound 10 was obtained as a colorless

solid in quantitative yield by dissolving 5 in THF and subsequently re-

moving all volatiles in vacuo. Colorless crystals suitable for an X-ray dif-

fraction experiments were obtained from a saturated solution of 10 in

hexane/THF (2:1). M.p. 266–2688C; ¹H NMR (300 MHz, 298 K, C₆D₆):

crystals of [BeI₂ACTHNUTRGNEUNG

(OEt₂)₂]:^[22]M.p. 48–498C; ¹H NMR (400 MHz, C₆D₆,

d=1.20 (d, ³J_HꢀH=6.9 Hz, 12H; CH

1.35 (brm_c, 12H; CH

CH(CH₃)₂), 3.58 (m_c, 4H; OCH₂CH₂), 4.82 (s, 1H; CH), 6.75–7.03 ppm

(m, 6H; Ar-H); ¹³C{¹H} NMR (75.5 MHz, 298 K, C₆D₆): d=24.3

(NCCH₃), 24.5 (CH(CH₃)₂), 25.1 (CH(CH₃)₂), 25.7 (OCH₂CH₂), 28.4 (br,

CH(CH₃)₂), 70.5 (br, OCH₂CH₂), 95.1 (CH), 124.2 (Ar-C), 125.8 (Ar-C),

G

298 K): d=1.05 (t, ³J_HꢀH=7.0 Hz, 12H; CH₂CH₃), 3.96 ppm (q, J_HꢀH

=

3

N

7.0 Hz, 8H; CH₂CH₃); ¹³C{¹H} NMR (100.6 MHz, C₆D₆, 298 K): d=13.8

(CH₃), 59.9 ppm (OCH₂); IR (Nujol): n˜ =1326 (m), 1190 (m), 1146 (m),

1091 (m), 1012 (m), 885 (m), 834 (m), 767 cm^ꢀ1(m). Data for

ACHTUNGTRENNUNG

1

A

U

[(^MesNacnac)BeI] 13: M.p. 199–2018C; H NMR (300 MHz, 298 K, C₆D₆):

N

d=1.55 (s, 6H; NCCH₃)_,2.08 (s, 12H; o-CH₃), 2.13 (s, 6H; p-CH₃), 4.80

(s, 1H; CH), 6.83 ppm (s, 4H; Ar-H); ¹³C{¹H} NMR (75.5 MHz, 298 K,

C₆D₆): d=19.3 (o-CH₃), 21.4 (p-CH₃), 22.3 (NCCH₃), 101.3 (CH), 130.1

(Ar-C), 132.4 (Ar-C), 136.0 (Ar-C), 143.1 (Ar-C), 168.6 ppm (NCCH₃);

IR (Nujol): n˜ =1607 (w), 1538 (s), 1376 (s), 1318 (m) 1239 (m), 1024 (s),

930 (s) 738 cm^ꢀ1(m); EIMS: m/z (%): 469.3 (45) [M⁺], 342.4 (100) [M⁺

ꢀI]; EI accurate mass calcd for C₂₃H₂₉N₂BeI: 469.1492; found: 469.1495.

CAUTION: Beryllium metal and its compounds are extremely toxic.

Suitable precautions (e.g., use of protective clothing, a breathing appara-

tus, and a well ventilated fume cupboard) should be taken for all manipu-

lations involving them. The reaction of beryllium metal with I₂in diethyl

ether can be rapid.

143.0 (br, Ar-C), 144.8 (Ar-C), 169.6 ppm (NCCH₃); IR (Nujol): n˜ =1621

(w), 1557 (m), 1455 (s), 1376 (s), 1313 (m), 1263 (m), 1174 (m), 1103 (m),

1056 (m), 1016 (s), 936 (m), 919 (m), 869 (m), 853 (m), 794 (s), 756 (s),

629 cm^ꢀ1(m); EIMS: m/z (%): 568.2 (4) [M⁺ꢀTHF], 418.4 (16)

[

^DippNacnacH⁺], 403.4 (42) [^DippNacnacH⁺ꢀCH₃], 202.3 (100) [MeCCN-

Dipp⁺].

[(^MesNacnac)MgI

ACHTUNGTRENNUNG(thf)] (11): Compound 11 was obtained as a colorless

solid in quantitative yield by dissolving 7 in THF and subsequently re-

moving all volatiles in vacuo. Colorless crystals suitable for an X-ray dif-

fraction experiments were obtained by recrystallizing 11 from a minimum

volume of THF. M.p. 218–2208C; ¹H NMR (300 MHz, 298 K, C₆D₆): d=

0.95 (brm_c, 4H; CH₂CH₂), 1.61 (s, 6H; NCCH₃), 2.15 (s, 6H; p-CH₃),

2.35 (brs, 12H; o-CH₃), 3.20 (brt, ³J_HꢀH=6.6 Hz, 4H; OCH₂CH₂), 4.90

(s, 1H; CH), 6.82 ppm (s, 4H; Ar-H); ¹³C{¹H} NMR (75.5 MHz, 298 K,

C₆D₆): d=19.6 (o-CH₃), 20.8 (p-CH₃), 23.1 (OCH₂CH₂), 24.7 (NCCH₃),

69.9 (OCH₂CH₃), 94.9 (CH), 129.4 (Ar-C), 132.2 (Ar-C), 133.6 (Ar-C),

144.9 (Ar-C), 168.7 ppm (NCCH₃); IR (Nujol): n˜ =1625 (w), 1556 (m),

1515 (m), 1258 (m), 1229 (s), 1200 (m), 1147 (m), 1098 (w), 1014 (m), 958

(vw), 920 (vw), 856 (m), 803 (w), 773 (w), 723 cm^ꢀ1 (w); EIMS: m/z (%):

[{(^DippNacnac)CaI

ACHTNUGTRNEUNG(OEt₂)}₂] (14): Iodine (1.22 g, 4.81 mmol) was added to

a mixture of freshly filed calcium metal (0.23 g, 5.74 mmol) in diethyl

ether (60 mL) at 208C. The resultant mixture was stirred vigorously for

7 days at 208C to give

[K(^DippNacnac)] (4.33 mmol, prepared in situ from the reaction of

^DippNacnacH with K[N

(SiMe₃)₂] in toluene) in a mixture of toluene

a fine white slurry. To this, a solution of

AHCTUNGTRENNUNG

(30 mL) and diethyl ether (10 mL) was slowly added at 208C. The resul-

tant mixture was stirred for 2 days and then filtered. Volatiles were re-

Chem. Eur. J. 2010, 16, 938 – 955

ꢀ 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

www.chemeurj.org

951

C. Jones, A. Stasch et al.

moved in vacuo and hexane (40 mL) added to the residue yielding a sus-

pension. Compound 14 was isolated by filtration as a colorless solid and

dried under vacuum (note that a 28% yield of the known complex,

[Ca(^DippNacnac)₂],^[28(b,c)]was crystallized from the hexane mother liquor).

Crystals of 14 that were suitable for X-ray structural analysis were ob-

tained by recrystallization from diethyl ether (yield=0.90 g, 32%).

(m), 1537 (m), 1493 (s), 1363 (s), 1310 (m), 1259 (m), 1213 (m), 1183 (m),

1153 (m), 1098 (s), 1020 (s), 932 (w), 873 (w), 798 (s), 777 (s), 708 (m),

694 (m), 667 cm^ꢀ1(m); EIMS: m/z (%): 1050.9 (1) [M⁺], 525.5 (42) [M/

2⁺], 502.5 (10) [^tBuNacnacH₂⁺], 445.4 (73) [^tBuNacnacH⁺ꢀC₄H₉]; elemen-

tal analysis calcd (%) for C₇₀H₁₀₆N₄Mg₂(M_r=1052.23): C 79.90, H 10.15,

N 4.62; found: C 79.65, H 10.02, N 4.77.

M.p.>3508C (decomp); ¹H NMR (400 MHz, 298 K, C₆D₆): d=0.94

[(^DippNacnac)Mg

1.55 mmol) and 7 (0.87 g, 1.55 mmol) were dissolved in toluene (50 mL).

The resultant solution was stirred over potassium mirror (0.70 g,

ACHTUNGTENR(NUNG m-H)ACHTUNGTRENNUNG 5 (1.00 g,

(m-I)Mg(^MesNacnac)] (18): Complex

3

(brm_c, 12H; OCH₂CH₃), 1.15 and 1.16 (two overlapping d, J_HꢀH

=

6.8 Hz, 24H; CH

(d, ³J_HꢀH=6.8 Hz, 12H; CH

16H; CH(CH₃)₂, OCH₂CH₃), 4.85 (s, 2H; CH), 7.06–7.18 ppm (m, 12H;

ArH); ¹³C{¹H} NMR (100.6 MHz, 298 K; C₆D₆): d=14.7 (OCH₂CH₃),

20.4, 22.7, 23.4, 24.2, 25.4 (4ꢂCH(CH₃)₂, 1ꢂCCH₃), 28.0 (CH(CH₃)₂),

28.4 (CH(CH₃)₂), 65.5 (OCH₂CH₃), 93.9 (CH), 123.0, 123.8, 124.8, 125.5,

A

ACHTUGNTRNEN(UNG CH₃)₂), 1.27

a

AHCTUNGTRENNUNG

17.9 mmol) for 24 h. The solution was filtered, volatiles were removed in

vacuo, and the residue was extracted into hot benzene. Yellow crystals of

18 were isolated from the solution upon cooling to 208C (yield=0.12 g,

8%). M.p. 147–1508C; ¹H NMR (300 MHz, 298 K, C₆D₆): d=1.11 (d,

ACHTUNGTRENNUNG

A

ACHTUNGTRENNUNG

³J_HꢀH=6.9 Hz, 12H; CH

(CH₃)₂), 1.14 (d, ³J_HꢀH=6.9 Hz; 12H, CH-

ACHTUNGTRENNUNG

136.0, 141.9 (ArC), 166.1 ppm (CCH₃); IR (Nujol): n˜ =1621 (m), 1552

(m), 1377 (s), 1261 (s), 1097 (s), 1019 (s), 866 (m), 797 (s), 758 cm^ꢀ1(m);

EIMS: m/z (%): 418.4 (33) [^DippNacnacH⁺], 403.4 (80) [^DippNacnacH⁺

ꢀCH₃], 202.3 (43) [MeCCNDipp⁺], 167.0 (100) [CaI⁺], 127.0 (50) [I⁺].

AHCTUNGTRENNUNG

3

NCCH₃), 2.30 (s, 6H; p-CH₃), 3.25 (sept, J_HꢀH=6.9 Hz, 4H; CHACHTUNGTRENNUNG(CH₃)₂),

3.92 (s, 1H; m-H), 4.80 (s, 1H; CH), 5.35 (s, 1H; CH), 6.57–7.25 ppm (m,

10H; Ar-H); ¹³C{¹H} NMR (75.5 MHz, 298 K, C₆D₆): d=21.2 (o-CH₃),

[MgACHTUNGTRENNUNG(

^PhNacnac)₂] (15): Method 1: Complex 6 (1.0 g, 2.1 mmol) was dis-

23.3 (p-CH₃), 23.8 (NCCH₃), 24.0 (NCCH₃), 24.4 (CCATHUNGTERN(NUNG CH₃)₂), 24.8 (C-

solved in toluene (50 mL). The solution was stirred over a potassium

mirror (0.70 g, 17.9 mmol) for 24 h at 208C. The resultant solution was fil-

tered and volatiles were removed in vacuo. The residue was dissolved in

hexane and the extract was cooled to ꢀ308C yielding yellow crystals of

15 overnight (yield=0.09 g, 16%). Method 2: MgnBu₂(1.0m solution in

heptane, 0.30 mL, 0.30 mmol) was added to a solution of ^PhNacnacH

(0.15 g, 0.60 mmol) in hexane (8 mL) at 208C. The mixture was stirred at

508C for 20 min, concentrated to ca. 1.5 mL, and cooled to 48C overnight

yielding 15 as large yellow crystals (yield=0.12 g, 76%). M.p. 131–

G

ACHTUNGTRENNUNG

C), 125.9 (Ar-C), 129.3 (Ar-C), 130.0 (Ar-C), 131.3 (Ar-C), 132.9 (Ar-C),

142.7 (Ar-C), 169.1 (NCCH₃), 169.9 ppm (NCCH₃); IR (Nujol): n˜ =1624

(m), 1555 (m), 1261 (m), 1022 (m), 854 (w), 798 cm^ꢀ1(m); EIMS: m/z

(%): 417.3 (35) [^DippNacnac⁺], 333.2 (8) [^MesNacnac⁺].

[Mg(^MesNacnac)₂] (19): Method 1: ^MesNacnacH (2.50 g, 7.5 mmol) was dis-

solved in toluene (20 mL). MgnBu₂(7.7 mmol, as a 1.0m solution in hep-

tane) was added and the resultant solution was stirred at 208C for 1 hr.

This was then heated at 608C for 2 h, and the volatiles were removed in

vacuo. The residue was dissolved in hexane (40 mL), PhSiH₃(1 mL,

0.88 g, 8.07 mmol) was added, and the solution was heated at reflux for

3 days. Colorless crystals of 19 were isolated from the reaction mixture

upon cooling to ꢀ308C (yield=0.90 g, 17%). Method 2: MgnBu₂(1.0m

solution in heptane, 0.79 mL, 0.79 mmol) was added to a solution of

^MesNacnacH (0.50 g, 1.49 mmol) in toluene (7 mL) at 208C. The mixture

was stirred at 508C for 1 h, then concentrated to ca. 2 mL. Hexane

(6 mL) was added and the mixture cooled to 48C, yielding 19 as colorless

crystals (yield=0.35 g, 68%). M.p. 260–2648C; ¹H NMR (300 MHz,

298 K, C₆D₆): d=1.55 (s, 12H; NCCH₃), 1.94 (s, 24H; o-CH₃), 2.22 (s,

12H; p-CH₃), 4.96 (s, 2H; CH), 6.76 ppm (s, 8H; Ar-H); ¹³C{¹H} NMR

(75.5 MHz, 298 K, C₆D₆): d=19.0 (o-CH₃), 21.2 (p-CH₃), 24.1 (NCCH₃),

96.8 (CH), 129.7 (Ar-C), 133.1 (Ar-C), 133.2 (Ar-C), 146.8 (Ar-

C),169.2 ppm (NCCH₃); IR (Nujol): n˜ =1611 (w), 1513 (s), 1253 (s), 1195

(s), 1146 (s), 1016 (s), 957 (w), 924 (w), 856 (s), 761 (m), 744 (m), 728

(m), 598 cm^ꢀ1(s); EIMS: m/z (%): 690.5 (100) [M⁺], 675.4 (40) [M⁺

1

1338C; H NMR (300 MHz, 298 K, C₆D₆): d=1.83 (s, 12H; NCCH₃), 4.81

(s, 2H; CH), 6.80–7.30 ppm (m, 20H; Ar-H); ¹³C{¹H} NMR (75.5 MHz,

298 K, C₆D₆): d=23.1 (NCCH₃), 96.8 (CH), 123.4 (Ar-C), 124.7 (Ar-C),

128.8 (Ar-C), 150.3 (Ar-C), 166.9 ppm (NCCH₃); IR (Nujol): n˜ =1634

(w), 1594 (m), 1551 (s), 1522 (s), 1261 (s), 1187 (s), 1169 (s), 1072 (s),

1021 (s), 932 (m), 905 (m), 834 (m), 802 (m), 750 (s), 698 (s), 661 (m),

630 (m), 614 cm^ꢀ1 (m); EIMS: m/z (%): 522.2 (10) [M⁺], 250.0 (50)

[

^PhNacnacH⁺]; elemental analysis calcd (%) for C₃₄H₃₄MgN₄(M_r=

522.97): C 78.09, H 6.55, N 10.71; found: C 77.47, H 6.51, N 10.49.

[(^MesNacnac)MgMg(^MesNacnac)] (16): Toluene (80 mL) and diethyl ether

(ca. 2 mL) were added to 7 (1.68 g, 1.52 mmol). The resultant solution

was rapidly stirred over a sodium mirror (0.70 g, 30.4 mmol) for 5 days to

yield a yellow-green suspension. This was filtered, the yellow filtrate was

concentrated to ca. 20 mL and placed at ꢀ308C overnight to give yellow

crystals of 16. A second crop of 16 was isolated after further concentra-

tion and cooling of the supernatant solution (yield=0.56 g, 51%). M.p.

1

201–2038C; H NMR (300 MHz, 298 K, C₆D₆): d=1.55 (s, 12H; NCCH₃),

ꢀMe], 334.2 (30)

[

^MesNacnacH⁺]; EI accurate mass calcd for

1.91 (s, 24H; o-CH₃), 2.30 (s, 12H; p-CH₃), 4.80 (s, 2H; CH), 6.86 ppm

(s, 8H; Ar-H); ¹³C{¹H} NMR (75.5 MHz, 298 K, C₆D₆): d=19.2 (o-CH₃),

21.2 (p-CH₃), 23.2 (NCCH₃), 95.4 (CH), 129.3 (Ar-C), 131.5 (Ar-C), 132.7

(Ar-C), 145.5 (Ar-C), 166.6 ppm (NCCH₃); IR (Nujol) n˜ =1624 (w), 1610

(w), 1526 (s), 1260 (s), 1197 (s), 1146 (s), 1016 (m), 958 (w), 854 (m), 727

(m), 693 cm^ꢀ1(w); EIMS: m/z (%): 715.2 (30) [M⁺], 690.3 (25)

[Mg(^MesNacnac)₂], 334.3 (40) [^MesNacnacH⁺]; elemental analysis calcd

(%) for C₄₆H₅₈Mg₂N₄(M_r=715.59): C 77.21, H 8.17%, N 7.83; found: C

76.42, H 8.19, N 7.66.

[(^tBuNacnac)MgMg(^tBuNacnac)] (17): A solution of 9 (0.65 g, 0.99 mmol)

in toluene (40 mL) was stirred vigorously for 16 h over a potassium

mirror (0.70 g, 17.9 mmol) at 208C. The resultant suspension was filtered,

the orange solution was concentrated under reduced pressure to ca.

20 mL, and then cooled to 58C overnight to give orange crystals of 17.

The supernatant was further concentrated at room temperature to ca.

10 mL and cooled to ꢀ308C to afford a second crop of 17 (yield=0.31 g,

59%). M.p. 278–2808C; ¹H NMR (300 MHz, 298 K, C₆D₆): d=0.96 (brd,

C₄₆H₅₈MgN₄: 690.4506; found: 690.4505; elemental analysis calcd (%) for

C₄₆H₅₈MgN₄(M_r=691.28): C 79.92, H 8.46, N 8.10; found: C 78.78, H

8.43, N 7.97.

[{Na(^tBuNacnac)}₂] (20): A solution of [{(^tBuNacnac)CaI

ACHTNUTRGNE(UNG thf)}₂] (0.70 g,

0.47 mmol) in toluene (50 mL) was stirred vigorously for 6 days over a

sodium mirror (0.420 g, 18.3 mmol) at 208C. The resultant suspension

was filtered, all volatiles were removed in vacuo, and the residue was ex-

tracted with benzene (30 mL). The brown-yellow filtrate was concentrat-

ed under reduced pressure to ca. 5 mL and yellow crystals of 20 were ob-

tained after 3 days upon standing at 208C (yield=0.25 g, 50%). M.p.

1

3

244–2528C; H NMR (300 MHz, 298 K, C₆D₆): d=1.10 (d, J_HꢀH=6.9 Hz,

12H; CH (CH₃)₂), 1.44 (s, 18H;

(CH₃)₂), 1.43 (d, ³J_HꢀH=6.9 Hz, 12H; CH

(CH₃)₃), 3.43 (sept, ³J_HꢀH=6.9 Hz, 4H; CH

(CH₃)₂), 4.99 (s, 1H; CH),

6.95–7.19 ppm (m, 6H; Ar-H); ¹³C{¹H} NMR (75.5 MHz, 298 K, C₆D₆):

d=23.6 (CH(CH₃)₂), 25.6 (CH(CH₃)₂), 27.5 (CH(CH₃)₂), 33.1 (C(CH₃)₃),

44.7 (C(CH₃)₃), 90.3 (CH), 119.2 (Ar-C), 123.5 (Ar-C), 137.2 (Ar-C),

151.8 (Ar-C), 168.5 ppm (CC(CH₃)₃); IR (Nujol): n˜ =1621 (m), 1548 (m),

G

ACHTUNGTRENNUNG

C

G

ACHTUNGTRENNUNG

A

R

ACHTUNGTRENNUNG

AHCTUNGTRENNUNG

³J_HꢀHca. 6.8 Hz, 24H; CH

³J_HꢀH=6.8 Hz, 24H; CH

(CH₃)₂), 3.30 (brsept, 8H; CH

2H; CH), 6.92–7.02 ppm (m, 12H; Ar-H); ¹³C{¹H} NMR (100.6 MHz,

298 K, C₆D₆): d=23.9 (CH(CH₃)₂), 27.0 (br, CH(CH₃)₂), 27.7 (CH(CH₃)₂,

32.9 (C(CH₃)₃), 43.6 (C(CH₃)₃), 96.8 (CH), 123.4 (Ar-C), 124.6 (Ar-C),

142.5 (Ar-C), 145.9 (Ar-C), 176.2 ppm (CC(CH₃)₃); IR (Nujol): n˜ =1621

ACHUTNGER(NGU CH₃)₂), 1.12 (s, 36H; CACHTUNGTRNE(UNNG CH₃)₃)_,1.34 (d,

AHCTUNGTRENNUNG

1325 (m), 1260 (s), 1215 (m), 1142 (m), 1095 (s), 1020 (s), 935 (m), 794

(s), 761 (m), 678 (cm)^ꢀ1(m); EIMS: m/z (%): 502.5 (10) [^tBuNacnacH₂⁺],

445.4 (96) [^tBuNacnacH⁺ꢀC₄H₉], 244.4 (100) [tBuCNDipp⁺]; elemental

analysis calcd (%) for C₃₅H₅₃N₂Na (M_r=524.80): C 80.10, H 10.18, N

5.34; found: C 79.27, H 10.30, N 5.21.

A

ACHTUNGTRENNUNG

A

R

ACHTUNGTRENNUNG

A

ACHTUNGTRENNUNG

AHCTUNGTRENNUNG

952

www.chemeurj.org

ꢀ 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Chem. Eur. J. 2010, 16, 938 – 955

Stabilized Mg^IDimers and Mg^IIHydride Complexes

FULL PAPER

[(^MesNacnac)Mg

(thf)Mg

E

131.3 (Ar-C), 132.5 (Ar-C), 133.0 (Ar-C), 145.2 (Ar-C), 168.6 ppm

(NCCH₃); IR (Nujol): n˜ =1624 (m), 1524 (s), 1396 (s), 1269 (s), 1220 (s),

1199 (m), 1101 (s), 1018 (s), 855 (m), 800 cm^ꢀ1(m); EIMS: m/z (%):

1068.4 (2) [M]⁺, 357.3 (100) [(^MesNacnac)Mg⁺], 334.3 (48) [^MesNacnacH⁺

]; elemental analysis calcd (%) for C₆₆H₈₈Mg₂N₁₀(M_r=1070.08): C 74.08,

H 8.29, N 13.08; found: C 73.05, H 8.46, N 12.32.

0.14 mmol) was dissolved in THF (5 mL) to give a red solution. Com-

pound 21 was isolated from the solution as red plates after concentrating

to ca. 2 mL and cooling to ꢀ308C (yield=0.094 g, 79%). M.p. 86–898C

(yellows with THF loss, then decomposes at 246–2488C); ¹H NMR

(300 MHz, 298 K, C₆D₆): d=1.38 (m_c, 8H; OCH₂CH₂), 1.56 (s, 12H;

NCCH₃), 1.98 (s, 24H; o-CH₃), 2.30 (s, 12H; p-CH₃), 3.44 (m_c, 8H;

OCH₂CH₂), 4.80 (s, 2H; CH), 6.88 ppm (s, 8H; Ar-H); ¹³C{¹H} NMR

(75.5 MHz, 298 K, C₆D₆): d=19.2 (o-CH₃), 20.9 (p-CH₃), 23.3 (NCCH₃),

25.4 (OCH₂CH₂), 68.1 (OCH₂CH₂), 94.6 (CH), 128.9 (Ar-C), 131.4 (Ar-

C), 131.9 (Ar-C), 146.9 (Ar-C), 165.2 ppm (NCCH₃); IR (Nujol): n˜ =1625

(w), 1608 (w), 1547 (m), 1400 (s), 1302 (w), 1260 (m), 1194 (m), 1144

(m), 1073 (m), 1019 (m), 958 (m), 915 (s), 876 (m), 853 (m), 802 (m), 740

(w), 696 cm^ꢀ1(s); EIMS: m/z (%): 334.3 (100) [^MesNacnacH⁺].

[(^MesNacnac)Mg(m-tBu₂N₂C₂O₂)Mg(^MesNacnac)]

(29):

tBuNCO

(0.035 mL, 0.030 g, 0.31 mmol) was added to a solution of 16 (0.10 g,

0.14 mmol) in toluene (14 mL) at ꢀ788C. The reaction mixture changed

color from yellow to colorless during the addition. It was warmed to

208C, volatiles were removed in vacuo and the residue was extracted

with hexane (20 mL). Colorless crystals of 29 were isolated upon cooling

of the solution to ꢀ308C overnight. A second crop of 29 was isolated

after further concentration and cooling of the supernatant solution (yield

0.02 g, 15%). ¹H NMR (300 MHz, 298 K, C₆D₆): d=0.87 (s, 12H; o-

[(^MesNacnac)Mg (DMAP)(^MesNacnac)] (22): Compound 16

ACHTUNGTRENNUNG(DMAP)MgACHTUGNTRENNUGN

(0.10 g, 0.14 mmol) was dissolved in toluene (15 mL). The solution was

cooled to ꢀ788C and DMAP (0.031 g, 0.25 mmol) was added. The reac-

tion mixture changed color from yellow to brown as it was warmed to

room temperature. Red-brown crystals of 22 were isolated from the reac-

tion mixture upon cooling to ꢀ308C. A second crop was isolated after

further concentration and cooling of the supernatant solution (yield

0.056 g, 36%). M.p. 142–1438C; ¹H NMR (300 MHz, 298 K, C₆D₆): d=

CH₃), 1.10 (s, 12H; o-CH₃), 1.23 (brs, 18H; CACHTGNUTERNU(NG CH₃)₃), 1.65 (s, 6H;

NCCH₃), 1.67 (s, 6H; NCCH₃), 2.07 (s, 6H; p-CH₃), 2.27 (s, 6H; p-CH₃),

4.94 (s, 1H; CH), 4.99 (s, 1H; CH), 6.82 (s, 4H; Ar-H), 6.83 ppm (s, 4H;

Ar-H); ¹³C{¹H} NMR (75.5 MHz, 298 K, C₆D₆): d=18.4 (o-CH₃), 19.3 (o-

CH₃), 20.7 (p-CH₃), 22.7 (p-CH₃), 22.9 (NCCH₃), 28.6 (NCCH₃), 31.8 (C-

ACHTUNERGN(UNG CH₃)₃), 51.9 (CCAHTUNGTERNN(UGN CH₃)₃), 94.4 (CH), 96.9 (CH), 128.8 (Ar-C), 129.2 (Ar-

C), 131.4 (Ar-C), 131.4 (Ar-C), 131.9 (Ar-C), 132.6 (Ar-C), 132.8 (Ar-C),

145.4 (Ar-C), 168.5 (NCCH₃), 168.6 ppm (NCCH₃); IR (Nujol):n˜ =1660

(w), 1584 (s), 1561 (m), 1542 (m), 1516 (m), 1394 (s), 1325 (m), 1307 (m),

1261 (m), 1222 (w), 1197 (m), 1146 (m), 1086 (w), 1015 (m), 981 (w), 952

(w), 852 (w), 801 cm^ꢀ1(w); EIMS: m/z (%): 912.4 (100) [M⁺], 334.4 (22)

1.74 (s, 12H; NCCH₃), 1.99 (s, 24H; o-CH₃), 2.19 (brs, 12H; NACTHNUTRGNEUNG(CH₃)₂),

2.33 (s, 12H; p-CH₃), 4.97 (s, 2H; CH), 6.01 (d, ³J_HꢀH=5.3 Hz, 4H;

DMAP Ar-H), 6.93 (s, 8H; Ar-H), 8.22 ppm (d, ³J_HꢀH=5.3 Hz, 4H;

DMAP Ar-H); ¹³C{¹H} NMR (75.5 MHz, 298 K, C₆D₆): d=19.6 (o-CH₃),

21.2 (p-CH₃), 23.8 (NCCH₃), 38.1 (N

N

[

^MesNacnacH⁺].

ACTHNUGTRNENUG

[(^tBuNacnac)Mg(m-H)₂Mg(^tBuNacnac)] (30): MgnBu₂(1.0m solution in

Ar-C), 128.9 (Ar-C), 131.2 (Ar-C), 132.1 (Ar-C), 148.5 (Ar-C), 150.0

(DMAP Ar-C), 154.2 (DMAP Ar-C), 164.6 ppm (NCCH₃); IR (Nujol):

n˜ =(cm^ꢀ1): 1621 (m), 1609 (m), 1538 (m), 1519 (m), 1409 (m), 1260 (m),

1224 (w), 1195 (m), 1144 (m), 1098 (w), 1008 (m), 950 (w), 854 (m), 807

(m), 757 (w), 727 (m), 668 (m); EIMS: m/z (%): 715.3 (30)

[{(^MesNacnac)Mg}₂⁺].

heptane, 4.10 mL, 4.10 mmol) was added to a solution of ^tBuNacnacH

(2.00 g, 3.98 mmol) in toluene (40 mL) and the mixture was heated to

1008C for 16 h. After cooling to room temperature, PhSiH₃(0.51 mL,

0.45 g, 4.18 mmol) was added and the mixture was heated at reflux for

48 h. After cooling, all volatiles were removed in vacuo and the residue

was extracted with hexane (50 mL). Concentration of the solution to ca.

25 mL and cooling to 58C yielded colorless crystals of 30 overnight. The

supernatant was further concentrated to ca. 10 mL and was cooled to

ꢀ308C to give a second crop of 30 (yield 0.83 g, 40%). M.p. 256–2588C;

[(^tBuNacnac)Mg

ACHTUNGTRENNUNG

(m-AdN₆Ad)Mg(^tBuNacnac)] (27): A solution of 1-azido-

ACHTUNGTRENNUNG

tion of 17 (0.050 g, 0.048 mmol) in toluene (15 mL) at ꢀ788C. An imme-

diate color change from orange to colorless occurred. The reaction mix-

ture was allowed to warm to room temperature and stirred for 1 h. It was

then filtered, concentrated to ca. 4 mL, and cooled to ꢀ308C overnight

yielding 27 as colorless crystals (yield 0.034 g, 51%). M.p. 292–2948C;

3

¹H NMR (300 MHz, 353 K, C₆D₆): d=1.12 (brd, J_HꢀHca. 6.8 Hz, 24H;

CH

(CH₃)₂), 3.26 (sept, ³J_HꢀH=6.8 Hz, 8H; CH

5.53 (s, 2H; CH), 6.95–7.02 ppm (m, 12H; Ar-H); ¹³C{¹H} NMR

(75.5 MHz, 298 K, C₆D₆): d=24.2 (br; CH(CH₃)₂), 26.4 (br; CH(CH₃)₂),

28.1 (CH(CH₃)₂), 33.2 (C(CH₃)₃), 44.2 (C(CH₃)₃, 96.8 (br; CH), 123.7

(Ar-C), 125.1 (br; Ar-C), 142.6 (br; Ar-C), 145.9 (br; Ar-C), 178.2 (br;

CC(CH₃)₃); IR (Nujol) n˜ =1537 (m), 149 (s), 1392 (s), 1364 (s), 1309 (m),

(CH₃)₃)_,1.30 (d, ³J_HꢀH=6.8 Hz, 24H; CH-

ACHTUGTNRENUNG(CH₃)₂), 1.16 (s, 36H; CAHCTUNGTRENNGUN

A

ACHTUGNTRENUN(GN CH₃)₂), 3.83 (s, 2H; MgH),

¹H NMR (300 MHz, 298 K, C₆D₆): d=0.47 (d, ³J_HꢀH=6.8 Hz, 12H; CH-

3

G

E

(CH₃)₂)_,

A

ACHTUNGTRENNUNG

(CH₃)₂), 1.51 (d, ³J_HꢀH=6.8 Hz, 12H;

A

R

ACHTUNGTRENNUNG

A

ACHTUNGTRENNUNG

1275 (m), 1256 (m), 1214 (m), 1184 (m), 1154 (m), 1099 (s), 1021 (m),

932 (w), 875 (w), 798 (m), 779 (s), 712 (m), 672 cm^ꢀ1(m); EIMS: m/z

(%): 502.6 (8) [^tBuNacnacH₂⁺], 445.6 (60) [^tBuNacnacH⁺ꢀC₄H₉], 224.3

(100) [C₁₇H₂₆N⁺]; elemental analysis calcd (%) for C₇₀H₁₀₈N₄Mg₂(M_r=

1054.24): C 79.75, H 10.33, N 5.31; found: C 78.99, H 10.43, N 4.91.

G

E

ACHTUNGTRENNUNG

AHCTUNGTRENNUNG

[(^tBuNacnac)Mg(H)

ACTHNUGRTENUNG(DMAP)] (31): DMAP (0.018 g, 0.142 mmol) was

1365 (m), 1260 (s), 1104 (s), 1060 (s), 1020 (s), 935 (m), 888 (m), 801 (s),

678 cm^ꢀ1(m); EIMS: m/z (%): 701.5 (6) [(M/2)⁺ꢀH], 502.5 (15)

added to a solution of 30 (0.075 g, 0.071 mmol) in toluene (9 mL) at 208C

and the mixture was stirred for 30 min. The reaction solution was concen-

trated to ca. 4 mL and cooled to ꢀ308C yielded colorless crystals of 31

overnight (yield 0.055 g, 60%). M.p. 160–1808C (decomp); ¹H NMR

[

^tBuNacnacH₂⁺], 445.6 (84) [^tBuNacnacH⁺ꢀC₄H₉], 224.3 (100) [C₁₇H₂₆N⁺].

ACHTUNGTRENNUNG

[(^MesNacnac)Mg(m-AdN₆Ad)Mg(^MesNacnac)] (28): 1-Azidoadamantane

(0.014 g, 0.08 mmol) in toluene (3 mL) was added to a solution of 16

(0.050 g, 0.07 mmol) in toluene (8 mL) at ꢀ788C. The yellow solution

changed to colorless during the addition. The resultant solution was

warmed to 208C, volatiles were removed in vacuo, and the residue was

dissolved in benzene (5 mL). Colorless crystals of 28 deposited from the

extract after it had been allowed to stand at room temperature overnight.

A second crop of 28 was isolated after further concentration of the super-

natant solution (yield 0.017 g, 27%). M.p. 180–1828C; ¹H NMR

(300 MHz, 298 K, C₆D₆): d=1.45–1.54 (m, 18H, Ad-CH; Ad-CH₂), 1.65

(s, 12H; NCCH₃), 1.88 (m_c, 12H; Ad-CH₂), 2.20 (s, 12H; p-CH₃), 2.25 (s,

12H; o-CH₃), 2.26 (s, 12H; o-CH₃), 4.83 (s, 2H; CH), 6.86 (s, 4H; Ar-H),

7.09 ppm (s, 8H; Ar-H) ; ¹³C{¹H} NMR (75.5 MHz, 298 K, C₆D₆): d=18.7

(o-CH₃), 18.9 (o-CH₃), 21.0 (p-CH₃), 23.3 (NCCH₃), 30.1 (Ad-C), 36.8

(Ad-C), 42.9 (Ad-C), 55.6 (Ad-C), 94.9 (CH), 129.1 (Ar-C), 129.5 (Ar-C),

(300 MHz, 298 K, C₆D₆): d=0.99 (brm_c, 6H; CH

(CH₃)₃)_,1.38–1.52 (brm, 12H; CH(CH₃)₂), 1.55 (brm_c, 6H; CH

1.90 (brs, 6H; N(CH₃)₂, 3.33 (brm_c, br, 2H; CH(CH₃)₂), 3.87 (brm_c, 2H;

CH(CH₃)₂), 4.65 (s, 1H; Mg-H), 5.64 (s, 1H; CH), 5.77 (brs, 2H; DMAP

m-Ar-H), 6.95–7.12 (m, 6H; Ar-H), 7.90 ppm (brs, 2H; DMAP o-Ar-H);

¹³C{¹H} NMR (75.5 MHz, 298 K, C₆D₆): d=21.2 (br; CH

(CH₃)₂), 23.2

(CH(CH₃)₂), 24.0 (br; CH(CH₃)₂), 25.0 (CH(CH₃)₂), 28.3 (br; CH(CH₃)₂),

28.8 (CH(CH₃)₂), 31.3 (C(CH₃)₃), 38.1 (N(CH₃)₂), 43.6 (C(CH₃)₂), 94.5

(CH), 106.7 (DMAP m-Ar-C), 122.8 (Ar-C), 123.0 (br; Ar-C), 123.7 (br;

Ar-C), 124.6 (Ar-C), 150.2 (DMAP p-Ar-C), 176.1 (CC(CH₃)₃(note that

ACHTUNGTRENNUNG

A

R

ACHTUNGTRENNUNG

A

ACHTUNGTRENNUNG

AHCTUNGTRENNUNG

A

E

N

ACHTUNGTRENNUNG

A

E

N

ACHTUNGTRENNUNG

AHCTUNGTRENNUNG

not all resonances are observed owing to peak broadening); IR (Nujol):

n˜ =1614 (s), 1537 (m), 1495 (m), 1365 (m), 1316 (m), 1261 (m), 1149 (m),

1096 (s), 1008 (s), 800 (s), 728 cm^ꢀ1(m); EIMSI m/z (%): 502.5 (10)

Chem. Eur. J. 2010, 16, 938 – 955

ꢀ 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

www.chemeurj.org

953

C. Jones, A. Stasch et al.

[

^tBuNacnacH₂⁺], 445.5 (84) [^tBuNacnacH⁺ꢀC₄H₉], 224.3 (100) [C₁₇H₂₆N⁺];

8744; b) X. Wang, L. Andrews, J. Phys. Chem. A 2004 , 108 , 1151 1 –

elemental analysis calcd (%) for C₄₂H₆₄N₄Mg (M_r=649.28): C 77.69, H

9.94, N 8.63; found: C 76.83, H 9.50, N 8.27.

11520.

2+

[4] It is of note that quasi Mg₂units have been reported to be present

Crystallography: Crystals of 6–20, 22, 27–31, and [(^MesNacnac)Mg

ACTHNUTRGNE(UNG m-

in the superconducting binary material, MgB₂, and related ternary

hydride materials such as Mg₄IrH₅. See, for example: R. B. King,

Polyhedron 2002 , 21 , 234 7 –2 350, and references therein.

I)₂Mg(^MesNacnac)] suitable for X-ray structural determination were

mounted in silicone oil. Crystallographic measurements were made by

using either a Nonius Kappa CCD or Bruker X8 CCD diffractometer

using a graphite monochromator with Mo_Karadiation (l=0.71073 ꢁ).

The data were collected at 123 K and the structures were solved by direct

methods and refined on F²by using full-matrix least-squares techniques

(SHELX97)^[52]and including all unique data. All non-hydrogen atoms

are anisotropic with hydrogen atoms (except hydrides) included in calcu-

lated positions (riding model). The hydride ligands in the crystal struc-

tures of compounds 18, 30, and 31 were refined with no positional re-

straints.

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Related magnesium(I) dimers, RMgMgX, have been proposed as in-

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A crystal of 16 that was suitable for a neutron diffraction experiment was

mounted in the helium flow cryostat of the instrument VIVALDI^[53]at

the Institut Laue-Langevin, Grenoble. Laue patterns were recorded from

the stationary crystal at a temperature of 123 K. The refinement of the

structure was undertaken by using the CRYSTALS^[54]suite of programs

and was commenced by using atomic positions of non-hydrogen atoms

taken from the X-ray crystal structure of the compound. After refine-

ment of this model, all hydrogen atoms were clearly visible from differ-

ence maps and were introduced into the model. Subsequent refinement

of the positional and isotropic displacement parameters for all atoms of

the structure led to its convergence with a final R(F) of 14.5% for 1993

independent reflections with [I>2s(I)]. In the final difference map for

the structure there was no significant residual nuclear density, which is

consistent with the absence of hydride ligands bridging the magnesium

centers of the compound. Full details of the neutron diffraction experi-

ment can be found in the Supporting Information.

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A table containing crystal data, details of data collections and refinement

for all compounds, selected metrical parameters and/or ORTEP diagrams

for the structures of 6, 10–12, 15, 19, 20, and [(^MesNacnac)Mg

ACTHNUTRGNE(UNG m-

I)₂(^MesNacnac)], as well as full details of the neutron diffraction experi-

ment on 16 can be found in the Supporting Information. CCDC-745078

(6), 745079 (7), 745080 (8), 745081 (9), 745082 (10), 745083 (11), 745084

(12), 745085 (13), 745086 (14), 745087 (15), 745088 (16: X-ray structure),

745089 (16: neutron structure), 745090 (17·toluene), 745091 (18), 745092

(19), 745093 (19·3benzene), 745094 (20), 745095 (22·3toluene), 745096

(27·2benzene), 745097 (28·3benzene), 745098 (29), 745099 (30·benzene),

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11945.

745100 (31·2benzene), and 745077 ([{(^MesNacnac)Mg

ACHTNUTRGENG(UN m-I)₂}₂]) contain the

supplementary crystallographic data for this paper. These data can be ob-

tained free of charge from The Cambridge Crystallographic Data Centre

via www.ccdc.cam.ac.uk/data_request/cif.

Acknowledgements

We thank the Australian Research Council (fellowships for C.J., A.S.,

and S.N. and a studentship for S.J.B.) and the US Air Force Asian office

of Aerospace Research and Development for funding. Funding from the

AMRF program of the Australian Nuclear and Technology Organisation

is acknowledged. Thanks also go to the EPSRC Mass Spectrometry Serv-

ice, Swansea, UK.

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2838.

[1] Of most relevance to this study is the chemistry of Group 13–15 ele-

ment(I) dimers, REER (R=bulky aryl, alkyl etc.,). For recent re-

views in this area, see: a) E. Rivard, P. P. Power, Inorg. Chem. 2007 ,

46 , 1004 7 –1 0064; b) P. P. Power, Organometallics 2007 , 26 , 436 2 –

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9223; Angew. Chem. Int. Ed. 2008 , 47 , 907 9 –9 083.

[2] See, for example: S. Petrie, Aust. J. Chem. 2003 , 56 , 25 9 –2 62, and

references therein.

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Chem. Eur. J. 2010, 16, 938 – 955

Stabilized Mg^IDimers and Mg^IIHydride Complexes

FULL PAPER

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yield amorphous materials, formulated as [{MgH₂(L)}_n]: M. Michal-

AHCTUNGTRENNUNG

[26] Theoretical studies have predicted significantly shorter and stronger

ACHTUNGTRENNUNG

ꢀ

Be Be bonds in compounds of the type RBeBeR (e.g., for R=Cp:

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[45] Another structurally characterized cluster compound exhibiting Mg-

Be Be distances of ca. 2.06–2.08 ꢁ; BDEs of ca. 70 kcalmol^ꢀ1) than

ꢀ

the Mg Mg bonds of magnesium(I) dimers RMgMgR (see Ref. [6]).

[27] See the Supporting Information for further details.

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₆ACHTUNGTRNENUG(IPr)₂{NACHTUNGTERNN(GUN SiMe₃)₂}₂] (IPr=:C-

AHCTUNGTRENNUNG

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[46] A good yield (76%) of the related complex [MgACHUTNGRNENUG(

^PhNacnac)₂] 15 can

[29] Theoretical studies have predicted significantly longer and weaker

similarly be obtained by treating ^PhNacnacH with MgnBu₂in hexane

at 508C for 20 min.

ꢀ

Ca Ca bonds in compounds of the type RCaCaR (Ca Ca distances

of ca. 3.73–3.82 ꢁ; BDEs of<30 kcalmol^ꢀ1) than the Mg Mg bonds

ꢀ

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[32] A very low yield (<2%) of the compound [(^tBuNacnac)Mg

G

ACHTUNGTRENNUNG

[D₆]benzene after several days. A poor-quality crystal structure of

the compound confirmed it to be monomeric in the solid state. No

spectroscopic data were obtained. The mechanism of formation of

this compound is unknown.

[33] The X-ray crystal structure of 21, although of low quality, ambigu-

ously revealed the connectivity of the compound and showed it to

have a similar geometry to that of 22.

[34] L. F. Sꢆnchez-Barba, D. L. Hughes, S. M. Humphrey, M. Bochmann,

Organometallics 2006, 25, 1012–1020.

Received: September 2, 2009

Published online: November 30, 2009

Chem. Eur. J. 2010, 16, 938 – 955

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www.chemeurj.org

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Article Doi

β-Diketiminate-Stabilized Magnesium(I) Dimers and Magnesium(II) Hydride Complexes: Synthesis, Characterization, Adduct Formation, and Reactivity Studies

DOI: 10.1002/chem.200902425

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