Copper chemistry of β-diketiminate ligands: Monomer/dimer equilibria and a new class of bis(μ-oxo)dicopper compounds

Inorg. Chem. 2002, 41, 6307−6321

Copper Chemistry of â-Diketiminate Ligands: Monomer/Dimer Equilibria

and a New Class of Bis(µ-oxo)dicopper Compounds

Douglas J. E. Spencer,^†Anne M. Reynolds,^†Patrick L. Holland,^†Brian A. Jazdzewski,^†

,|

Carole Duboc-Toia,^†,‡Laurent Le Pape,^§Seiji Yokota,^|Yoshimitsu Tachi,^|Shinobu Itoh,* and

,†

William B. Tolman*

Department of Chemistry and Center for Metals in Biocatalysis, UniVersity of Minnesota,

207 Pleasant Street SE, Minneapolis, Minnesota 55455, Laboratoire des Champs Magnetiques

Intenses, 25 AV. des Martyrs, BP 166, CEA-Grenoble, F-38042 Grenoble Cedex 9, France,

Laboratoire de Physico-chimie des Me´taux en Biologie, FRE 2427 CEA-CNRS-UJF, De´partement

Re´ponse et Dynamique Cellulaires, CEA-Grenoble, 38054 Grenoble Cedex 9, France, and

Department of Chemistry, Graduate School of Science, Osaka City UniVersity, 3-3-138 Sugimoto,

Sumiyoshi-ku, Osaka 558-8585, Japan

Received May 29, 2002

A series of Cu(I) and Cu(II) complexes of a variety of â-diketiminate ligands (L^-) with a range of substitution

patterns were prepared and characterized by spectroscopic, electrochemical, and, in several cases, X-ray

crystallographic methods. Specifically, complexes of the general formula [LCuCl]₂were structurally characterized

and their magnetic properties assessed through EPR spectroscopy of solutions and, in one instance, by variable-

temperature SQUID magnetization measurements on a powder sample. UV−vis spectra indicated reversible

dissociation to 3-coordinate monomers LCuCl in solution at temperatures above −55 °C. The Cu(I) complexes

LCu(MeCN) exhibited reversible Cu(I)/Cu(II) redox couples with E_1/2values between +300 and +520 mV versus

NHE (cyclic voltammetry, MeCN solutions). These complexes were highly reactive with O , yielding intermediates

2

that were identified as rare examples of neutral bis(µ-oxo)dicopper complexes on the basis of their EPR silence,

diagnostic UV−vis absorption data, and O-isotope-sensitive resonance Raman spectroscopic features. The structural

features of the compounds [LCuCl]₂and LCu(MeCN) as well as the proclivity to form bis(µ-oxo)dicopper products

upon oxygenation of the Cu(I) complexes are compared to data previously reported for complexes of more sterically

hindered â-diketiminate ligands (Aboelella, N. W.; Lewis, E. A.; Reynolds, A. M.; Brennessel, W. W.; Cramer, C.

J.; Tolman, W. B. J. Am. Chem. Soc. 2002, 124, 10600. Spencer, D. J. E.; Aboelella, N. W.; Reynolds, A. M.;

Holland, P. L.; Tolman, W. B. J. Am. Chem. Soc. 2002, 124, 2108. Holland, P. L.; Tolman, W. B. J. Am. Chem.

Soc. 1999, 121, 7270). The observed structural and reactivity differences are rationalized by considering the steric

influences of both the substituents on the flanking aromatic rings and those present on the â-diketiminate backbone.

Introduction

toward this goal has been attained through examination of

the dioxygen reactivity of synthetic Cu(I) complexes, which

has resulted in the characterization of a variety of biologically

relevant superoxo, µ-peroxo, and bis(µ-oxo) copper complex

topologies (cf. Figure 1).²A key research objective has been

to comprehend how supporting ligand structural features

influence the relative stabilities and interconversions of these

species, with recent emphasis on ligand effects on the

Understanding the nature of reactive intermediates that

form upon reaction of O₂with Cu(I) centers in proteins is

critical for developing structure/function relationships in

metallobiochemistry and catalysis.¹Considerable progress

* To whom correspondence should be addressed. E-mail: shinobu@

scisv.sci.osaka-cu.ac.jp (S.I.); tolman@chem.umn.edu (W.B.T.). Fax: 612-

624-7029 (W.B.T.).

^†University of Minnesota.

(1) (a) Solomon, E. I.; Sundaram, U. M.; Machonkin, T. E. Chem. ReV.

1996, 96, 2563-2605. (b) Klinman, J. P. Chem. ReV. 1996, 96, 2541-

2561. (c) Solomon, E. I.; Chen, P.; Metz, M.; Lee, S.-K.; Palmer, A.

E. Angew. Chem., Int. Ed. 2001, 40, 4570-4590.

^‡Laboratoire des Champs Magnetiques Intenses, CEA-Grenoble.

^§Laboratoire de Physico-chimie des Me´taux en Biologie, CEA-Grenoble.

^|Osaka City University.

Published on Web 11/08/2002

Inorganic Chemistry, Vol. 41, No. 24, 2002 6307

Spencer et al.

Figure 1. Observed geometries of mono- and dicopper intermediates

formed in reactions of Cu(I) complexes with O₂.

equilibrium between (µ-η²:η²-peroxo)dicopper(II,II) and bis-

(µ-oxo)dicopper(III,III) units³that are relevant to proposed

metalloprotein active site intermediates.^1,4We and others

showed that both of these units could be supported by neutral,

multidentate N-donor ligands and that ligand structural

elements (e.g., size of substituents, macrocycle ring size,

denticity) play a critical role in determining which unit(s)

formed and how it (they) reacted.^2,3,5More recently, we began

to examine the O₂reactivity of Cu(I) complexes of â-diketim-

inate ligands, which have been used extensively in coordina-

tion chemistry⁶and have been applied lately toward the

isolation of novel low-coordinate metalloprotein active site

models comprising Cu(II)⁷and Fe(I or II).⁸In preliminary

communications,⁹the characterization of novel monomeric

Figure 2. â-Diketiminate ligands used in this work, with the abbreviation

system indicated. Note that when R′′′ ) H, this substituent will be omitted

-

from the ligand abbreviation (e.g. H(Me₂L^iPr2

) Pr, and R′′′ ) H).

)

for R ) H, R′ ) Me, R′′

i

1:1 O₂adducts or bis(µ-oxo)dicopper compounds supported

by â-diketiminates comprising identical 2,6-diisopropyl-

phenyl flanking groups but disparate backbone substituents,

H(R′₂L^iPr2)^-(R′ ) Me or ^tBu) and Ph(H₂L^iPr2)^-, respectively,

were described (see Figure 2 for ligand abbreviation scheme).

Herein, we report the results of studies of the Cu(I) and

Cu(II) chemistry of an expanded set of â-diketiminates with

variable substituent arrays. An analysis of the structures of

complexes of the general formula [LCuCl]_n(n ) 1 or 2)

and LCu(MeCN) has shed light on the steric effects of the

(2) Recent reviews: (a) Blackman, A. G.; Tolman, W. B. In Metal-Oxo

and Metal-Peroxo Species in Catalytic Oxidations; Meunier, B., Ed.;

Springer-Verlag: Berlin, 2000; Vol. 97, pp 179-211. (b) Kopf, M.-

A.; Karlin, K. D. In Biomimetic Oxidations Catalyzed by Transition

Metal Complexes; Meunier, B., Ed.; Imperial College Press: London,

2000; pp 309-362. (c) Karlin, K. D.; Zuberbu¨hler, A. D. In

Bioinorganic Catalysis, 2nd ed.; Reedijk, J., Ed.; Marcel Dekker: New

York, 1999; pp 469-534. (d) Mahadevan, V.; Gebbink, R. J. M. K.;

Stack, T. D. P. Curr. Opin. Chem. Biol. 2000, 4, 228-234. (e) Que,

L., Jr.; Tolman, W. B. Angew. Chem., Int. Ed. 2002, 41, 1114-1137.

(3) (a) Tolman, W. B. Acc. Chem. Res. 1997, 30, 227-237. (b) Holland,

P. L.; Tolman, W. B. Coord. Chem. ReV. 1999, 190-192, 855-869.

(c) Mahadevan, V.; Henson, M. J.; Solomon, E. I.; Stack, T. D. P. J.

Am. Chem. Soc. 2000, 122, 10249-10250. (d) Lam, B. M. T.; Halfen,

J. A.; Young, V. G., Jr.; Hagadorn, J. R.; Holland, P. L.; Lledo´s, A.;

Cucurull-Sa´nchez, L.; Novoa, J. J.; Alvarez, S.; Tolman, W. B. Inorg.

Chem. 2000, 39, 4059-4072. (e) Cahoy, J.; Holland, P. L.; Tolman,

W. B. Inorg. Chem. 1999, 38, 2161-2168. (f) Pidcock, E.; DeBeer,

S.; Obias, H. V.; Hedman, B.; Hodgson, K. O.; Karlin, K. D.; Solomon,

E. I. J. Am. Chem. Soc. 1999, 121, 1870-1878. (g) Obias, H. V.;

Lin, Y.; Murthy, N. N.; Pidcock, E.; Solomon, E. I.; Ralle, M.;

Blackburn, N. J.; Neuhold, Y.-M.; Zuberbu¨hler, A. D.; Karlin, K. D.

J. Am. Chem. Soc. 1998, 120, 12960-12961. (h) Hayashi, H.;

Fujinami, S.; Nagatomo, S.; Ogo, S.; Suzuki, M.; Uehara, A.;

Watanabe, Y.; Kitagawa, T. J. Am. Chem. Soc. 2000, 122, 2124-

2125. (i) Liang, H.-C.; Zhang, C. X.; Henson, M. J.; Sommer, R. D.;

Hatwell, K. R.; Kaderli, S.; Zuberbu¨hler, A. D.; Rheingold, A. L.;

Solomon, E. I.; Karlin, K. D. J. Am. Chem. Soc. 2002, 124, 4170-

4171. (j) Hayashi, H.; Uozumi, K.; Fujinami, S.; Nagatomo, S.; Shiren,

K.; Furutachi, H.; Suzuki, M.; Uehara, A.; Kitagawa, T. Chem. Lett.

2002, 416-417.

(6) Selected recent examples: (a) Kakliou, L.; Scanlon, W. J., IV; Qian,

B.; Baek, S. W.; Smith, M. R., III. Inorg. Chem. 1999, 38, 5964-

5977 and references therein. (b) Chamberlain, B. M.; Cheng, M.;

Moore, D. R.; Ovitt, T. M.; Lobkovsky, E. B.; Coates, G. W. J. Am.

Chem. Soc. 2001, 123, 3229-3238. (c) Stender, M.; Eichler, B. E.;

Hardman, N. J.; Power, P. P.; Prust, J.; Noltemeyer, M.; Roesky, H.

W. Inorg. Chem. 2001, 40, 2794-2799. (d) Hardman, N. J.; Power,

P. P. J. Am. Chem. Soc. 2001, 40, 2474-2475. (e) MacAdams, L. A.;

Kim, W.-K.; Liable-Sands, L. M.; Guzei, I. A.; Rheingold, A. L.;

Theopold, K. H. Organometallics 2002, 21, 952-960. (f) Prust, J.;

Hohmeister, H.; Stasch, A.; Roesky, H. W.; Magull, J.; Alexopoulos,

E.; Uso´n, I.; Schmidt, H.-G.; Noltemeyer, M. Eur. J. Inorg. Chem.

2002, 2156-2162. (g) Harder, S. Organometallics 2002, 21, 3782-

3787.

(7) (a) Holland, P. L.; Tolman, W. B. J. Am. Chem. Soc. 1999, 121, 7270-

7271. (b) Holland, P. L.; Tolman, W. B. J. Am. Chem. Soc. 2000,

122, 6331-6332. (c) Randall, D. W.; DeBeer, S.; Holland, P. L.;

Hedman, B.; Hodgson, K. O.; Tolman, W. B.; Solomon, E. I. J. Am.

Chem. Soc. 2000, 122, 11632-11648. (d) Jazdzewski, B. A.; Holland,

P. L.; Pink, M.; Young, V. G., Jr.; Spencer, D. J. E.; Tolman, W. B.

Inorg. Chem. 2001, 40, 6097-6107.

(4) (a) Decker, H.; Dillinger, R.; Tuczek, F. Angew. Chem., Int. Ed. 2000,

39, 1591-1595. (b) Holland, P. L.; Rodgers, K. R.; Tolman, W. B.

Angew. Chem., Int. Ed. 1999, 38, 1139-1142.

(5) (a) Taki, M.; Itoh, S.; Fukuzumi, S. J. Am. Chem. Soc. 2001, 123,

6203-6204. (b) Itoh, S.; Kumei, H.; Taki, M.; Nagatomo, S.;

Kitagawa, T.; Fukuzumi, S. J. Am. Chem. Soc. 2001, 123, 6708-

6709. (c) Itoh, S.; Taki, M.; Nakao, H.; Holland, P. L.; Tolman, W.

B.; L. Que, J.; Fukuzumi, S. Angew. Chem., Int. Ed. 2000, 39, 398-

400. (d) Mahadevan, V.; DuBois, J. L.; Hedman, B.; Hodgson, K. O.;

Stack, T. D. P. J. Am. Chem. Soc. 1999, 121, 5583-5584. (e) Pidcock,

E.; Obias, H. V.; Abe, M.; Liang, H. C.; Karlin, K. D.; Solomon, E.

I. J. Am. Chem. Soc. 1999, 121, 1299-1308. (f) Kodera, M.;

Katayama, K.; Tachi, Y.; Kano, K.; Hirota, S.; Fujinami, S.; Suzuki,

M. J. Am. Chem. Soc. 1999, 121, 11006-11007.

(8) (a) Smith, J. M.; Lachicotte, R. J.; Holland, P. L. Chem. Commun.

2001, 1542-1543. (b) Smith, J. M.; Lachicotte, R. J.; Pittard, K. A.;

Cundari, T. R.; Lukat-Rodgers, G.; Rodgers, K. R.; Holland, P. L. J.

Am. Chem. Soc. 2001, 123, 9222-9223. (c) Andres, H.; Bominaar,

E. L.; Smith, J. M.; Eckert, N. A.; Holland, P. L.; Mu¨nck, E. J. Am.

Chem. Soc. 2002, 124, 3012-3025.

(9) (a) Spencer, D. J. E.; Aboelella, N. W.; Reynolds, A. M.; Holland, P.

L.; Tolman, W. B. J. Am. Chem. Soc. 2002, 124, 2108-2809. (b)

Aboelella, N. W.; Lewis, E. A.; Reynolds, A. M.; Brennessel, W. W.;

Cramer, C. J.; Tolman, W. B. J. Am. Chem. Soc. 2002, 124, 10660-

10661.

6308 Inorganic Chemistry, Vol. 41, No. 24, 2002

Copper Chemistry of â-Diketiminate Ligands

Scheme 1

ligand substituent pattern. These effects are related to the

reactivity of the Cu(I) species with O₂at low temperature.

For the â-diketiminates used here, rare examples of neutral

bis(µ-oxo)dicopper complexes¹⁰are formed, which have been

characterized by UV-vis, EPR, and resonance Raman

spectroscopy. While this work was in progress, a Cu(I)

complex of H(Me₂L^Me2)^-was reported to react with O₂to

yield a bis(µ-hydroxo)dicopper(II,II) complex, and the

intermediacy of an unstable bis(µ-oxo) species was sug-

gested.¹¹In addition, a polymeric â-diketiminate Cu(I)

species, [NO₂(H₂L^Me2Me)Cu]_n,¹²a derived monomeric phos-

phine adduct,¹²and the oxidative degradation of Cu(II) and

Zn(II) complexes of H(Me₂L^Me2Me)^-were described.¹³

Results and Discussion

Ligand Syntheses. A variety of â-diketimines with

variable backbone and aryl substituents, R(R′₂L^{R′′2R′′′})H, were

prepared to probe the influence of ligand structural variation

on copper ion complexation and Cu(I)/O₂chemistry (Figure

2). Of these, NO₂(H₂L^Me2Me)H¹²and H(Me₂L^R′′2)H (R′′ )

Me or Et)¹⁴were reported previously. The compound Cl-

(Me₂L^Me2)H was prepared via the typical Schiff base

condensation method,^6,15here involving reaction of 2,6-

dimethylaniline with 3-chloro-2,4-pentanedione. The syn-

theses of the remaining â-diketimines incorporating aryl units

at the central backbone position began from the vinami-

dinium hexafluorophosphate salts derived from reaction of

the appropriate arylacetic acid with POCl₃and DMF at 70

°C (Scheme 1).^16,17The salts were hydrolyzed by refluxing

in a basic solution to give the respective dialdehydes (in

enolized form) as brown oils. These brown oils were reacted

without further purification with the appropriate aniline

derivative to provide the desired â-diketimines, which were

isolated as yellow crystalline solids. All new â-diketimines

were characterized by ¹H and ¹³C NMR spectroscopy, high-

resolution mass spectrometry, and elemental analysis. Depro-

0.8THF,¹⁸where L ) H(Me₂L^Et2)^-, Cl(Me₂L^Me2)^-, or

Ph(H₂L^iPr2)^-. X-ray crystal structures of the complexes

comprising the first two ligands are shown in Figure 3, with

crystallographic data and selected bond lengths and angles

listed in Tables 1 and 2, respectively. Most notably, the dif-

fraction data indicate dinuclear structures for the green com-

pounds, which contain 4-coordinate Cu(II) ions bridged by

two chloride ligands. On the basis of spectroscopic similari-

ties (vide infra), an analogous structure is likely for the com-

plex supported by Ph(H₂L^iPr2)^-. These structures are distinct

from those reported previously for the compounds supported

by H(Me₂L^{iPr2 -}and Cl(Me₂L^iPr2)^-, both of which are

)

n

mononuclear with 3-coordinate Cu(II) centers.^7a,dConsistent

with their higher coordination numbers, the metal-ligand

bond distances in the dinuclear complexes are longer than

those in the mononuclear species (average Cu-Cl ) 2.32

Å vs 2.12 Å, Cu-N ) 1.93 Å vs 1.87 Å). The coordination

geometries of the metal ions in the dicopper complexes are

distorted from tetragonal toward tetrahedral, as indicated by

N-Cu-N/Cl-Cu-Cl dihedral angles of 51.78(4)° for

[Cl(Me₂L^Me2)CuCl]₂and 50.05(7)° for [H(Me₂L^Et2)CuCl]₂.¹⁹

Such values that are intermediate between those of the

tetragonal and tetrahedral extremes (0 and 90°, respectively)

have been reported for other Cu(II) systems.²⁰Although

similar in most respects, the structures of the dicopper

compounds differ from each other with respect to the relative

tonation with BuLi in either pentane or THF yielded the

lithium salts of the â-diketiminate ligands, which were

isolated as solids for storage in the glovebox and subsequent

use for preparing copper complexes. In some cases the salts

1

retained a THF solvent molecule, as shown by H and ¹³C

NMR spectroscopy.

Syntheses and Properties of Cu(II) Complexes. We

prepared several Cu(II) complexes [LCuCl]₂by treatment

of selected lithium â-diketiminates with anhydrous CuCl₂‚

(10) A surprisingly stable neutral bis(µ-oxo)dicopper complex supported

by an anionic iminophosphinamide ligand has been reported: Straub,

B. F.; Rominger, F.; Hofmann, P. Chem. Commun. 2000, 1611-1612.

(11) Dai, X.; Warren, T. H. Chem. Commun. 2001, 1998-1999.

(12) Yokota, S.; Tachi, Y.; Nishiwaki, N.; Ariga, M.; Itoh, S. Inorg. Chem.

2001, 40, 5316-5317.

(13) Yokota, S.; Tachi, Y.; Itoh, S. Inorg. Chem. 2002, 41, 1342-1344.

(14) Cheng, M.; Moore, D. R.; Reczek, J. J.; Chamberlain, B. M.;

Lobkovsky, E. B.; Coates, G. W. J. Am. Chem. Soc. 2001, 123, 8738-

8749.

(15) For example, see: (a) Clegg, W.; Cope, E. K.; Edwards, A. J.; Mair,

F. S. Inorg. Chem. 1998, 37, 2317-2319 and references therein. (b)

Stender, M.; Wright, R. J.; Eichler, B. E.; Prust, J.; Olmstead, M. M.;

Roesky, H. W.; Power, P. P. J. Chem. Soc., Dalton Trans. 2001, 3465-

3469 and references therein.

(17) Davies, I. W.; Marcoux, J.-F.; Wu, J.; Palucki, M.; Corley, E. G.;

Robbins, M. A.; Tsou, N.; Ball, R. G.; Dormer, P.; Larsen, R. D.;

Reider, P. J. J. Org. Chem. 2000, 65, 4571-4574.

(18) So, J.-H.; Boudjouk, P. Inorg. Chem. 1990, 29, 1592-1593.

(19) This value for [H(Me₂L^Et2)CuCl]₂corresponds to the major (85%)

component of the disordered structure. The value for the minor

component is 51.75(17)°. For details, see the Experimental Section

and the Supporting Information (CIF file).

(16) The procedure used was adapted from one kindly provided to us by

R. F. Jordan, University of Chicago.

(20) For example, see: Knapp, S.; Keenan, T. P.; Zhang, X.; Fikar, R.;

Potenza, J.; Schugar, H. J. J. Am. Chem. Soc. 1990, 112, 3452-3464.

Inorganic Chemistry, Vol. 41, No. 24, 2002 6309

Spencer et al.

simulated the features between 2000 and 4500 G (dotted line

overlay in Figure 5a) using parameters for an S ) 1 sys-

tem with g₁) 2.11(1), g₂) 2.15(1), g₃) 2.16(2), D )

0.156(1) cm^-1, and E ) 3(7) × 10^-4cm^-1(line widths W_x

) 23(2) mT, W_y) 10.5(5) mT, W_z) 21(3) mT). The low-

field signal (g ) 4.9) corresponds to a ∆M_S) (2 transition,

which was not simulated.²¹The EPR data are consistent with

the retention in solution of the bis(µ-chloro)dicopper(II,II)

structure determined by X-ray crystallography. In addition,

a small amount (ca. 10% by integration) of a monomeric

Cu(II) species in solution is indicated by the weak signal at

g ≈ 2 (presumably Cl(Me₂L^Me2)CuCl; vide infra).

EPR spectra of toluene solutions of [Ph(H₂L^iPr2)CuCl]₂

(Figure 5b) and [H(Me₂L^Et2)CuCl]₂(Figure 5c) also contain

signals attributable to dinuclear species (cf. the low-field ∆M_S

) (2 features), but with additional features at g ≈ 2.0. In

the spectrum of the latter complex the signal is axial with g_|

) 2.20, g ) 2.05, and A^Cu) 128 × 10^-4cm^-1. These

|

parameters and, in particular, the signature low A^Cuvalue,

|

closely match those previously measured for the monomeric

complexes LCuCl (L ) H(Me₂L^iPr2)^-or Cl(Me₂L^iPr2)^-).^7a,d

For example, the spectrum of H(Me₂L^iPr2)CuCl is character-

ized by g_|) 2.20, g ) 2.05, and A^Cu_|) 130 × 10^-4cm^-1.

Evidently, [H(Me₂L^Et2)CuCl]₂exists to a significant extent

as H(Me₂L^Et2)CuCl at low temperature in toluene solution,

suggesting the existence of an equilibrium between mono-

and dinuclear forms of this complex (Scheme 2).

Support for this notion was provided by UV-vis data

that were obtained over a range of temperatures for the

chloro-bridged complexes. For example, solid samples of

[H(Me₂L^Et2)CuCl]₂are green, yet solutions in toluene or

CH₂Cl₂are deep purple. UV-vis spectra of these purple

solutions (Figure 6a) are invariant over -50 °C < T < 25

°C and are essentially identical to that of the monomeric

Figure 3. X-ray crystal structure representations of (a) [Cl(Me₂L^Me2)-

CuCl]₂and (b) [H(Me₂L^Et2)CuCl]₂. All atoms are shown as (a) 50% or (b)

35% thermal ellipsoids with only heteroatoms labeled and hydrogen atoms

omitted for clarity.

3-coordinate complexes supported by H(Me₂L^{iPr2 -}

or

)

Cl(Me₂L^iPr2)^-(cf. dashed line in Figure 6a).^7a,dThese data

show that while dinuclear as a solid, [H(Me₂L^Et2)CuCl]₂

dissociates essentially entirely upon dissolution to H(Me₂L^Et2)-

CuCl under these conditions, with the EPR data (Figure 5c)

showing the presence of both mono- and dinuclear forms in

solution at lower temperatures (20 K). The relative stabilities

of the mono- and dinuclear forms are shifted for the systems

orientations of their â-diketiminates, as seen most readily

by comparing the views down their respective Cu-Cu

vectors (Figure 4). In [H(Me₂L^Et2)CuCl]₂, the â-diketimi-

nate N donors are “eclipsed” (Figure 4b), whereas in

[Cl(Me₂L^Me2)CuCl]₂they are “staggered” (Figure 4a). Ob-

servation of the latter conformation is perhaps most signifi-

cant, for it illustrates how interligand repulsions (i.e., between

the aryl rings) may be alleviated in â-diketiminate-supported

dicopper complexes that contain single-atom bridges.

In one case, [Cl(Me₂L^Me2)CuCl]₂, the resultant magnetic

moment as a function of temperature (5-300 K) and applied

magnetic field (0.5-5 T) was measured for a powder sample

using a SQUID magnetometer (Figure S1, Supporting

Information). The data indicate only very weak antiferro-

magnetic coupling between the Cu(II) ions, with a fit to the

0.5 T data using the Van-Vleck formula (as described in the

Experimental Section) yielding J ) -0.3(1) cm^-1, g )

2.04(1), and t ) 5(1) × 10^-5cm³mol^-1. The X-band EPR

spectrum of a frozen solution of the complex in toluene at

20 K is shown in Figure 5a. Signals centered at g ) 4.9,

2.5, 1.8, and 1.5 dominate the spectrum. The observation of

such signals is consistent with the small J value and

population of an S ) 1 state at 20 K. We successfully

supported by Ph(H₂L^{iPr2 -}and Cl(Me₂L^Me2)^-, as indicated

)

by temperature-dependent UV-vis spectra, exemplified for

the latter case in Figure 6b. At 22.5 °C, only spectral features

diagnostic for the 3-coordinate monomer are evident (dotted

line), but at -55.0 °C the spectrum is significantly different,

with new bands at ∼480 and ∼690 nm (solid line). Interme-

diate spectra were obtained at temperatures between these

extremes, and the spectral changes were fully reversible.

These data are consistent with the presence of an equilibrium

between [Cl(Me₂L^Me2)CuCl]₂and Cl(Me₂L^Me2)CuCl, the di-

nuclear species with features at 480 and 690 nm being

favored at lower temperatures. Similar data that support the

same conclusion were obtained for [Ph(H₂L^iPr2)CuCl]₂(Fig-

ure S2).^9a

(21) Pilbrow, J. R. Transition Ion Electron Paramagnetic Resonance;

Clarendon Press: Oxford, U.K., 1990; Chapter 7.

6310 Inorganic Chemistry, Vol. 41, No. 24, 2002

Copper Chemistry of â-Diketiminate Ligands

Table 1. Summary of X-ray Crystallographic Data

[Ph(H₂L^iPr2)Cu(MeCN)]^a

[3,5-(CF₃)₂C₆H₃(H₂L^iPr2)Cu(MeCN)]^a

[H(Me₂L^Me2)Cu(CNC₆H₃Me₂)]^a

empirical formula

fw

C₃₅H₄₄CuN₃

570.27

C₃₇H₄₄CuF₆N₃

706.28

C₃₀H₃₃ClCuN₃

534.58

cryst system

space group

a (Å)

b (Å)

c (Å)

R (deg)

â (deg)

γ (deg)

V (Å³)

monoclinic

Cc

9.927(3)

20.216(5)

16.489(5)

90

96.031(4)

90

3290.8(16)

4

triclinic

P1h

monoclinic

P2₁/c

11.7422(18)

11.4347(6)

20.519(3)

90

97.356(7)

90

2732.4(6)

4

9.4815(18)

13.068(3)

14.499(3)

96.998(3)

95.087(3)

94.424(3)

1769.0(6)

2

Z

D

_calc(g cm^-3

)

1.151

1.326

1.299

cryst dimens

1.33 × 0.63 × 0.15

2.01-25.03

0.689

22 831

5548

0.20 × 0.15 × 0.15

1.42-25.07

0.678

12 604

6219

0.25 × 0.25 × 0.15

1.75-25.05

0.920

13 114

4814

θ range (deg)

abs coeff (mm^-1

reflcns collcd

unique reflcns

params

)

372

467

324

R1, wR2 (for I > 2σ(I))^c

goodness-of-fit

0.0381, 0.1010

0.988

0.606, -0.341

0.0558, 0.1424

1.046

0.411, -0.587

0.0374, 0.0885

1.007

0.478, -0.426

largest peak, hole (e/Å^-3

)

a

b

[Cl(Me₂L^Me2)CuCl]₂

[H(Me₂L^Et2)CuCl]₂

[NO₂(H₂L^Me2Me)Cu(OH)₂]^b

empirical formula

fw

C₄₂H₄₈Cu₂Cl₄N₄

877.72

C₅₀H₆₆Cu₂N₄Cl₂

921.05

C₄₂H₅₀Cu₂N₆O₆

861.99

cryst system

space group

a (Å)

b (Å)

c (Å)

R (deg)

â (deg)

γ (deg)

V (Å³)

monoclinic

C2/c

18.9825 (5)

11.6252 (2)

20.3111 (5)

90

114.6590 (10)

90

4073.42 (16)

4

monoclinic

P2₁/n

13.6615 (9)

12.5107 (8)

15.1162 (10)

90

109.2870 (10)

90

2438.6 (3)

2

orthorhombic

Pbcn

21.4089(6)

8.0931(2)

24.2109(7)

90

4194.9(2)

4

1.365

Z

D

_calc(g cm^-3

)

1.431

1.254

cryst dimens

0.4 × 0.4 × 0.15

2.11-24.97

1.342

10 141

3576

0.5 × 0.4 × 0.3

2.38-25.04

1.018

18 235

4299

0.5 × 0.2 × 0.2

2.1-27.5

1.067

9618

3128

θ range (deg)

abs coeff (mm^-1

reflcns collcd

unique reflcns

params

)

241

284

279

R1, wR2 (for I > 2σ(I))^c

goodness-of-fit

0.0242, 0.0637

1.033

0.263, -0.362

0.0339, 0.0980

0.997

0.356, -0.230

0.0340, 0.0450

1.025

0.40, -0.42

largest peak, hole (e/Å^-3

)

2

^aStructures determined at T ) -100 °C. ^bStructures determined at T ) +20 °C. ^cR1 ) Σ||F_o| - |F_c|/|F_o|; wR2 ) [Σw(F_o²- F_c)²/Σw(F_o)²]^1/2, where

2

w ) 1/[σ²(F_o+ (aP)²+ bP], P ) (F_o+ 2F_c)/3, and a and b are constants given in the Supporting Information.

Taken together, the structural and spectroscopic results

reported previously^7,9aand described herein for the series

[LCuCl]_n(n ) 1 or 2, L ) â-diketiminate) provide important

experimental measures of the steric influences of the sup-

porting ligands. Those ligands with backbone R-substituents

Syntheses and Structures of Cu(I) Complexes. With

only a few exceptions, reaction of the lithium â-diketiminates

with [Cu(MeCN)₄]CF₃SO₃in THF yielded Cu(I) complexes

of the general formula LCu(MeCN) that were isolated as

yellow solids (Scheme 3). One exception was [NO₂(H₂L^Me2Me)-

Cu(MeCN)], which was synthesized in situ by the addition

of MeCN to [NO₂(H₂L^Me2Me)Cu]_n.¹²In the case of Cl-

(Me₂L^Me2)H, reaction of its lithium salt with [Cu(MeCN)₄]-

CF₃SO₃invariably resulted in disproportionation, as evi-

denced by coloration of the reaction solution (dark brown)

and the appearance of a dark red precipitate. The only route

to a Cu(I) complex of this ligand that we have found so far

involves treating Cl(Me₂L^Me2)H with [CuCH₂SiMe₃]₄²²in the

presence of an aryl isocyanide “trap”, CNC₆H₃Me₂, to yield

i

and aryl Pr groups (e.g., H(Me₂L^iPr2)^-, Cl(Me₂L^iPr2)^-, and

H(tBu₂L^iPr2)^-) are sufficiently encumbered to prevent dimer-

ization and to yield only monomeric 3-coordinate species

LCuCl (n ) 1). Ligands with either smaller aryl groups or

which lack backbone R-substituents (e.g., H(Me₂L^Et2)^-,

Cl(Me₂L^Me2)^-, and Ph(H₂L^iPr2)^-) yield complexes that are

dinuclear (n ) 2) in the solid state and at low temperature

in solution but which are prone to dissociation to monomeric

species in solution at higher temperatures. These â-diketimi-

nate ligand steric differences that are the basis for the

structural variances in the compounds [LCuCl]_nalso underly

differences in the structures and O₂reactivity of Cu(I)

complexes, as discussed below.

(22) (a) Lappert, M. F.; Pearce, R. Chem. Commun. 1973, 24-25. (b) Jarvis,

J. A.; Kilbourn, B. T.; Pearce, R.; Lappert, M. F. Chem. Commun.

1973, 475-476. (c) Jarvis, J. A. J.; Pearce, R.; Lappert, M. F. J. Chem.

Soc., Dalton Trans. 1977, 999-1003.

Inorganic Chemistry, Vol. 41, No. 24, 2002 6311

Spencer et al.

Table 2. Selected Interatomic Distances (Å) and Angles (deg)^a

[Ph(H₂L^iPr2)Cu(MeCN)]

Cu-N1

1.964(2)

1.860(3)

128.19(11)

Cu1-N5

N5-Cu1-N1

N5-Cu1-N1S

1.950(2)

97.25(9)

133.75(10)

Cu-N1S

N1-Cu1-N1S

[3,5-(CF₃)₂C₆H₃(H₂L^iPr2)Cu(MeCN)]

Cu1-N1

1.908(3)

1.862(4)

97.59(11)

106.86(15)

152.9(5)

Cu1-N5

1.977(3)

1.977(17)

155.09(15)

101.4(5)

57.7(5)

Cu1-N1S

N1-Cu1-N5

N5-Cu1-N1S

N1-Cu1-N1S

N1S-Cu1-N1S

[Cl(Me₂L^Me2)Cu(CNC₆H₃Me₂)]

Cu1-N1

1.931(2)

1.824(3)

137.64(10)

176.0(2)

Cu1-N2

N1-Cu1-N2

N2-Cu1-C22

1.954(2)

95.51(8)

126.84(10)

Cu1-C22

N1-Cu1-C22

Cu1-C22-N3

[Cl(Me₂L^Me2)CuCl]₂

Cu1-N1

1.9223(15)

2.3319(5)

3.3763(4)

94.67(6)

Cu1-N2

1.9194(15)

2.3092(5)

100.47(5)

100.39(5)

143.67(5)

86.631(18)

Cu1-Cl1

Cu1-Cl1′

Cu1-Cu1′

N1-Cu1-N2

N1-Cu1-Cl1

N2-Cu1-Cl1

N1-Cu1-Cl1′

N2-Cu1-Cl1′

Cl1-Cu1-Cl1′

143.58(5)

[H(Me₂L^Et2)CuCl]₂

Cu1-N1

1.9297(18)

2.3274(7)

3.4243(5)

146.02(7)

99.12(6)

Cu1-N2

1.9295(19)

2.3194(7)

95.59(8)

100.83(6)

143.48(7)

85.06(3)

Cu1-Cl1

Cu1-Cl1′

Cu1-Cu1′

N1-Cu1-N2

N1-Cu1-Cl1′

N2-Cu1-Cl1′

Cl1-Cu1-Cl1′

N1-Cu1-Cl1

N2-Cu1-Cl1

Cl1-Cu1-Cl1′

85.06(3)

[NO₂(H₂L^Me2Me)Cu(µ-OH)₂]

Cu1-O3

1.905(2)

1.934(2)

2.341(4)

163.27(11)

Cu1-N1

1.940(2)

3.005(1)

96.7(1)

94.3(1)

Cu1-N2

Cu1-Cu1′

O3-Cu1-N1

N1-Cu1-N2

O3-O3′

O3-Cu1-N2

^aEstimated standard deviations in parentheses. “S” refers to atoms of

bound solvent molecules, and prime symbols refer to symmetry-related

atoms (see CIF for details).

Figure 5. EPR spectra of (a) [Cl(Me₂L^Me2)CuCl]_nin toluene, 9.600 GHz,

20 K, with simulation overlaid as dotted line (see text for parameters), (b)

[Ph(H₂L^iPr2)CuCl]_nin toluene, 9.614 GHz, 20 K, and (c) [H(Me₂L^Et2)CuCl]_n

in toluene, 9.590 GHz, 4 K. The annotations are approximate g values

obtained from inspection.

Scheme 2

Figure 4. Views along the Cu-Cu vectors of the X-ray structures of (a)

[Cl(Me₂L^Me2)CuCl]₂and (b) [H(Me₂L^Et2)CuCl]₂. The â-diketiminate back-

bone and backbone substituent atoms have been omitted for clarity.

1

isolable Cu(I) complexes were characterized by H NMR

and UV-vis spectroscopy, elemental analysis, and, in three

instances, by X-ray crystallography. In general, the spectral

data are unremarkable and are consistent with the formulated

[Cl(Me₂L^Me2)Cu(CNC₆H₃Me₂)], which was isolated as a light

yellow crystalline solid. This compound and the other

6312 Inorganic Chemistry, Vol. 41, No. 24, 2002

Copper Chemistry of â-Diketiminate Ligands

Scheme 3

distances in other Cu(I)-â-diketiminate complexes (1.90-

1.99 Å)^7d,9,11,12but longer than in 3-coordinate Cu(II)-â-dike-

timinate species (1.86-1.90 Å) as expected on the basis of

the metal oxidation level.⁷The structures are generally similar

to previously reported analogues supported by the more

sterically encumbered ligands H(Me₂L^iPr2)^-or H(tBu₂L^iPr2)^-,⁹

but there is a noteworthy difference involving the orientation

of the ⁱPr groups. In [H(Me₂L^iPr2)Cu(MeCN)], the ⁱPr group

methine hydrogen atoms point inward toward the â-diketimi-

nate ligand in an orientation typical for complexes of

H(Me₂L^iPr2)^-.^6-9Steric interactions between the backbone

Figure 6. (a) UV-vis spectra of [H(Me₂L^Et2)CuCl]_nin toluene at 22.4

°C (s) and -49.8 °C (‚‚‚), overlaid with the spectrum of H(Me₂L^iPr2)CuCl

in CH₂Cl₂(- - -).^7a(b) UV-vis spectra of [Cl(Me₂L^Me2)CuCl]₂in toluene

at 22.4 °C (‚‚‚) and -55.0 °C (s).

i

methyl and the Pr groups presumably are responsible for

structures, but it is worth noting that those complexes that

contain a central methine â-diketiminate backbone substituent

(R) exhibit an intense electronic absorption feature that is

sensitive to the nature of the R group (Table 3). Thus, an

absorption band at λ_max≈ 380 nm (ꢀ ≈ 20 000 M^-1cm^-1/

Cu) for the compounds with R ) Ph appears at ∼15 nm

longer wavelength than for the complexes with R ) 3,5-

(CF₃)₂C₆H₃. The energy, intensity, and sensitivity of this

feature to the electron-withdrawing capability of the R group

are consistent with an assignment as a â-diketiminate ligand-

based π f π* transition.^7c

Representations of the X-ray crystal structures of

[Ph(H₂L^iPr2)Cu(MeCN)], [3,5-(CF₃)₂C₆H₃(H₂L^iPr2)Cu(MeCN)],

and [Cl(Me₂L^Me2)Cu(CNC₆H₃Me₂)] are shown in Figure 7,

with selected crystallographic data and interatomic distances

and angles listed in Tables 1 and 2, respectively. The Cu(I)

centers generally exhibit 3-coordinate, planar, approxi-

mately C_2V-symmetric geometries, as indicated by sums of

N-Cu-N angles equal to 360 ( 1° and approximately equal

N-Cu-N_MeCNor N-Cu-C angles (∆ values e 11°).²³The

one exception is [3,5-(CF₃)₂C₆H₃(H₂L^iPr2)Cu(MeCN)], in

which the MeCN ligand is disordered over two positions

(84:16 ratio) characterized by large ∆ values (48 and 52°),

resulting in a site symmetry significantly distorted from C_2V.

The average Cu-N(â-diketiminate) bond distance among the

three compounds is 1.95 Å, within the range of analogous

this conformational preference. In contrast, in [Ph(H₂L^iPr2)-

Cu(MeCN)] and [3,5-(CF₃)₂C₆H₃(H₂L^iPr2)Cu(MeCN)] that

lack the â-diketiminate backbone methyl groups, one or more

i

of the Pr groups are rotated away from this orientation by

i

up to 180° (cf. bottom left Pr group in Figure 7a).

Recognizing the possible impact of ill-defined crystal packing

forces, we nonetheless hypothesize that the presence of these

alternate rotomers indicates greater ⁱPr group conformational

flexibility that results in decreased effective steric bulk in

these systems relative to those that contain an R-alkyl group,

such as H(Me₂L^iPr2)^-. These notions are further supported

by the reactivity results described below.

Electrochemistry of Cu(I) Complexes. Cyclic voltam-

metry experiments were performed on solutions of the

Cu(I) complexes in MeCN with 0.1 M Bu₄NPF₆at room

temperature. All the compounds exhibit a reversible anodic

wave when scanned initially to either reductive or oxidative

potential, with i_a≈ i_band values of E_pa- E_pcin the range

78-110 mV that do not vary as a function of scan rate

between 100 and 350 mV s^-1(cf. Figure S3). We attribute

this wave to the Cu(I)/Cu(II) redox couple. The values for

E_1/2(vs NHE)²⁴are listed in Table 4.²⁵The low potentials

reflect the strong electron-donating capability of the â-diketim-

inate ligands;^7cby comparison, potentials reported for other

(24) The values vs NHE were obtained by adding 640 mV to the value

measured versus Fc/Fc⁺in CH₃CN with Bu₄NPF₆as electrolyte,

according to Table 1 in the following: Connelly, N. G.; Geiger, W.

E. Chem. ReV. 1996, 96, 877-910.

(23) ∆ ) the difference between the N-Cu-N_MeCNor N-Cu-C angles.

For example, for [Ph(H₂L^iPr2)Cu(MeCN)], ∆ ) |( N1-Cu1-N1S)

- ( N5-Cu1-N1S)| ) |128.19(11)° - 133.75(10)°| ) 5.6°.

(25) In the cathodic region each complex exhibited an irreversible reduction.

Inorganic Chemistry, Vol. 41, No. 24, 2002 6313

Spencer et al.

Table 3. Spectroscopic Properties of Cu(I) Complexes and Derived Bis(µ-oxo)dicopper Intermediates^a

UV-vis λ_max(nm)

resonance Raman ν(Cu₂O₂)

ligand

(ꢀ, M^-1cm^-1) of Cu(I) complex

(ꢀ, M^-1cm^-1) of intermediate

(cm^-1) of intermediate

H(Me₂L^Et2

)

348 (27 000)

340 (20 000)

426 (10 000),^b352 (22 000), 332 (sh, 27 000)

422 (11 000),^b344 (sh, 32 000), 328 (37 000)

433 (sh, 7600),^b369 (20 000)

604 (577)

608 (581)

580 (560)

591/617 (574)

586/614 (573)

574/581 (563)

592/607/613 (573)

586/618 (575)

580/617 (573)

599/624 (582)^d

H(Me₂L^Me2

Ph(H₂L^iPr2

)

378 (21 000), 298 (36 000)

381 (21 000), 298 (36 000)

378 (19 000), 298 (25 000)

365 (sh, 19 000), 328 (31 000)

366 (sh, 19 000), 328 (34 000)

365 (sh, 21 000), 331 (26 000)

366 (sh, 20 000), 324 (36 000)

381 (24 600)^c

Ph(H₂L^Et2

Ph(H₂L^Me2

3,5-(CF₃)₂C₆H₃(H₂L^iPr2

3,5-(CF₃)₂C₆H₃(H₂L^Et2

3,5-(CF₃)₂C₆H₃(H₂L^Me2

3,5-(CF₃)₂C₆H₃(H₂L^CH3,CD3

NO₂(H₂L^Me2Me

)

425 (16 500),^b379 (20 000)

)

420 (12 200),^b377 (19 000)

)

433 (15 500),^b360 (sh, 21 000), 312 (35 000)

423 (13 200),^b361 (sh, 18 000), 318 (26 000)

417 (19 700),^b361 (sh, 21 000), 317 (29 000)

416 (16 200),^b361 (sh, 20 000), 314 (35 000)

440 (≈17 800)^b,c

)

^aExcept as noted, all UV-vis and Raman spectra were measured in THF, with extinction coefficents reported per Cu. Except as noted, UV-vis spectra

of the oxygenated intermediates were obtained at -80 °C and resonance Raman spectra were obtained at -196 °C using 457.9 nm laser excitation. Only

¹⁸O-sensitive vibrations in Raman spectra are quoted with data acquired using ¹⁸O₂listed in parentheses. ^bThis extinction coefficient reported per bis(µ-

oxo)dicopper complex to facilitate comparison to literature values. ^cMeasured in MeCN at -40 °C. ^dData obtained at -196 °C on MeCN solutions.

Table 4. Values of E_1/2for â-Diketiminate-Copper Complexes

E_1/2

∆E_P

entry

complex

(mV)^d(mV)^d

ref

1

2

3

4

5

6

7

8

9

[H(Me₂L^iPr2)Cu(MeCN)]^a

[H(Me₂L^Et2)Cu(MeCN)]^a

[H(Me₂L^Me2)Cu(MeCN)]^a,b

[Ph(H₂L^iPr2)Cu(MeCN)]^a

[Ph(H₂L^Et2)Cu(MeCN)]^a

[Ph(H₂L^Me2)Cu(MeCN)]^a

+425

+343

+309

95 this work

84 this work

74 this work

+384 105 this work

+420 100 this work

+388 100 this work

[3,5-(CF₃)₂C₆H₃(H₂L^iPr2)Cu(MeCN)]^a+449 110 this work

[3,5-(CF₃)₂C₆H₃(H₂L^Et2)Cu(MeCN)]^a+428

95 this work

[3,5-(CF₃)₂C₆H₃(H₂L^Me2)Cu(MeCN)]^a+400 106 this work

10 [NO₂(H₂L^Me2Me)Cu(MeCN)]^a

+520

-80

-180

-260

-280

78 this work

70 7a

80 7a

79 7d

76 7d

11 [H(Me₂L^iPr2)CuCl]^c

12 [H(Me₂L^iPr2)CuSCPh₃]^c

13 [H(Me₂L^iPr2)CuOC₆H₄Bu]^c

t

14 [H(Me₂L^iPr2)CuOC₆H₄OMe]^c

^aAll values reported vs NHE, by adding 640 mV to the value measured

vs the ferrocene/ferrocenium couple in CH₃CN (+0.642 V vs Ag wire)

with Bu₄NPF₆as electrolyte.¹⁹^bFor this compound, the E_1/2value shifted

over multiple runs, a degree of irreproducibility that suggests that the redox

process may be more complex than for the other systems. ^cMeasured in

THF with Bu₄NPF₆as electrolyte, cited vs NHE. ^dMeasurements at a scan

rate of 100 mV s^-1

.

measured for a range of â-diketiminate Cu(II) halide,

phenoxide, and thiolate complexes (entries 11-14).⁷Effects

of â-diketiminate ligand substituent variation in otherwise

alike compounds are apparent, but they are generally small.

For example, comparison of the data in entries 4 and 7 for

complexes with ligands that are identical except for the

central â-diketiminate backbone substituent (Ph vs 3,5-

(CF₃)₂C₆H₃) reveals a shift of +65 mV as the electron-

withdrawing capability of the substituent increases. De-

creased shifts for the same backbone substituent comparison

are observed when the R′′ groups are smaller (e.g., +8 mV

for entries 5 and 8, +12 mV for entries 6 and 9). Finally,

the influence of the nitro group is most significant, as the

potential for [NO₂(H₂L^Me2Me)Cu(MeCN)] (entry 10) is ≈100

mV more anodic than for the other Cu(I) complexes. All of

these potential shifts are consistent with decreased stabiliza-

tion of the Cu(II) state relative to the Cu(I) state as the strong

electron donation by the â-diketiminate is modulated by

electron withdrawing substituents. Importantly, however, the

differences in E_1/2values among the Cu(I) compounds listed

Figure 7. X-ray crystal structure representations of (a) [Ph(H₂L^iPr2)Cu-

(MeCN)], (b) [3,5-(CF₃)₂C₆H₃(H₂L^iPr2)Cu(MeCN)], and (c) [Cl(Me₂L^Me2)-

Cu(CNC₆H₃Me₂)]. All atoms are shown as 50% thermal ellipsoids with

only heteroatoms labeled (except for the fluorine atoms in (b)), and hydrogen

atoms are omitted for clarity.

three coordinate Cu(I) complexes with neutral N-donors and

MeCN ligands are significantly more positive (by ca. +0.5

V).²⁶Additional anionic coligands depress the E_1/2values

further, as reflected by the data for Cu(II)/Cu(I) couples

(26) Yates, P. C.; Drew, M. G. B.; Trocha-Grimshaw, J.; McKillop, K. P.;

Nelson, S. M.; Ndifon, P. T.; McAuliffe, C. A.; Nelson, J. J. Chem.

Soc., Dalton Trans. 1991, 1973-1979.

6314 Inorganic Chemistry, Vol. 41, No. 24, 2002

Copper Chemistry of â-Diketiminate Ligands

Figure 8. UV-vis absorption spectra of THF solutions at -80 °C of [3,5-

(CF₃)₂C₆H₃(H₂L^iPr)Cu(MeCN)] (‚‚‚) and the product of its oxygenation

(s). The extinction coefficient (y axes) for the product are per bis(µ-oxo)-

dicopper complex.

Figure 9. X-ray crystal structure representation of [{NO₂(H₂L^Me2Me)Cu}₂-

(µ-OH)₂]. All atoms are shown as 50% thermal ellipsoids with only

heteroatoms labeled and hydrogen atoms and solvent molecules omitted

for clarity (except for the hydrogen atoms on the hydroxo bridge).

in Table 4 do not correlate with differences in the course of

their reactions with O₂(vide infra).

analogy to the Cu(I) cases, we assign the intense high-energy

feature as a â-diketiminate-based π f π* transition. As ob-

served for the Cu(I) complex precursors, this band is sensitive

to the â-diketiminate R group and shifts to shorter wave-

length as the electron-withdrawing capability of the R group

is increased. As a result, the ≈420 nm band appears as a

largely obscured shoulder when R ) Ph and is more readily

discerned for R ) 3,5-(CF₃)₂C₆H₃(Figure 8). The nature of

the R group does not affect the ∼420 nm feature signifi-

cantly, suggesting that this charge transfer band does not

involve the â-diketiminate ligand in any significant way.

Instead, the energy and intensity of this feature are reminis-

cent of those of a band with oxo f Cu(III) CT character

that is firmly associated with bis(µ-oxo)dicopper com-

plexes.^2e,3,29,30

To corroborate this electronic absorption spectral assign-

ment and the conclusion that the intermediates are indeed

bis(µ-oxo)dicopper species, we collected resonance Raman

spectra of frozen THF solutions using an excitation wave-

length of 457.9 nm at -196 °C. Spectra were acquired on

samples prepared with ¹⁶O₂or ¹⁸O₂to conclusively identify

vibrational features involving incorporated oxygen atoms.

Numerous resonance-enhanced features were observed, but

only a few in the 550-625 cm^-1range were found to be

O-isotope sensitive; these are listed in Table 3. Illustrative

spectra of the intermediates derived from [3,5-(CF₃)₂C₆H₃-

(H₂L^Me2)Cu(MeCN)] and [Ph(H₂L^iPr2)Cu(MeCN)] are shown

in Figure 10, and plots of all spectra are presented in Figure

S4.

Dioxygen Reactivity. The Cu(I) complexes prepared in

this work are exceedingly air sensitive. Treatment of solu-

tions of the complexes in THF with O₂at -80 °C induced

a color change to golden-brown or green; representative

UV-vis spectral changes are shown in Figure 8. A sim-

ilar reaction was observed upon oxygenation of [NO₂-

(H₂L^Me2Me)Cu(MeCN)] in MeCN at -40 °C. The oxy-

genated species were EPR silent (frozen solution, X-band,

2-20 K). Bubbling of argon through the intermediate

solutions at low-temperature did not induce spectral changes,

indicating that the oxygenation process is irreversible under

the conditions used. Spectrophotometric titration data for the

reaction of [Ph(H₂L^iPr2)Cu(MeCN)] showed a Cu:O₂stoi-

chiometry of 2.0(2):1. In an alternate route, addition of 1-5

equiv of a 1:1 solution of H₂O₂(aq) (31.3%) and Et₃N to a

solution of [Ph(H₂L^iPr2)CuCl]_nin THF or toluene at -40 °C

yielded UV-vis spectral features similar to those seen upon

oxygenation of [Ph(H₂L^iPr2)Cu(MeCN)]. No reaction of the

Cu(II) precursor with H₂O₂was observed in the absence of

NEt₃. All of the intermediate solutions changed color upon

warming yet remained essentially EPR silent,²⁷signifying

conversion to a magnetically coupled dicopper(II,II) species.

In one instance, with the ligand NO₂(H₂L^Me2Me)^-, a bis(µ-

hydroxo)dicopper(II,II) complex was isolated from the

decomposed solution and was structurally characterized by

X-ray crystallography (Figure 9). The â-diketiminates adopt

an eclipsed conformation, similar to that of [H(Me₂L^Et2)-

CuCl]₂(Figure 4b). In general, the structure is unexceptional,

being rather similar to those of previously reported complexes

of this type.^11,28

For the system supported by Ph(H₂L^iPr2)^-(Figure 10b), a

single peak appears at ∼580 cm^-1which shifts by -20 cm^-1

when ¹⁸O₂is used. We assign this feature as an A_gsymmetry

[Cu₂(µ-O)₂]²⁺core vibration by analogy to published data

on bis(µ-oxo)dicopper complexes.^2e,3,29An identical spec-

The UV-vis spectra of the colored intermediate solutions

contain intense bands at λ_max≈ 380 nm (ꢀ ≈ 20 000 M^-1

cm^-1/Cu) and ≈ 425 nm (ꢀ ≈ 10 000-20 000 M^-1cm^-1/

dicopper complex), as well as a broad, weak band at λ_max

≈

600 nm (ꢀ ≈ 100 M^-1cm^-1/Cu) (Figure 8 and Table 3). By

(29) (a) Henson, M. J.; Mukherjee, P.; Root, D. E.; Stack, T. D. P.;

Solomon, E. I. J. Am. Chem. Soc. 1999, 121, 10332-10345. (b)

Holland, P. L.; Cramer, C. J.; Wilkinson, E. C.; Mahapatra, S.;

Rodgers, K. R.; Itoh, S.; Taki, M.; Fukuzumi, S.; Que, L., Jr.; Tolman,

W. B. J. Am. Chem. Soc. 2000, 122, 792-802.

(30) Mahadevan, V.; Hou, Z.; Cole, A. P.; Root, D. E.; Lal, T. K.; Solomon,

E. I.; Stack, T. D. P. J. Am. Chem. Soc. 1997, 119, 11996-11997.

(27) An axial signal from a monocopper(II) species was observed for the

warmed solutions, but values for spin quantitation were only between

1 and 7% (versus an external standard).

(28) Mahapatra, S.; Halfen, J. A.; Wilkinson, E. C.; Pan, G.; Wang, X.;

Young, V. G., Jr.; Cramer, C. J.; Que, L., Jr.; Tolman, W. B. J. Am.

Chem. Soc. 1996, 118, 11555-11574.

Inorganic Chemistry, Vol. 41, No. 24, 2002 6315

Spencer et al.

Figure 11. Resonance Raman spectra (λ_ex) 457.9 nm, -196 °C) of THF

solutions of the intermediates resulting from the reactions of [3,5-

(CF₃)₂C₆H₃(H₂L^CH3,CD3)Cu(MeCN)] (s) and [3,5-(CF₃)₂C₆H₃(H₂L^Me2)Cu-

(MeCN)] (‚‚‚) with (a) ¹⁶O₂and (b) ¹⁸O₂.

Figure 10. Resonance Raman spectra (λ_ex) 457.9 nm, -196 °C) of THF

solutions of the intermediates resulting from the reactions of ¹⁶O₂(s) or

¹⁸O₂(‚‚‚) with (a) [3,5-(CF₃)₂C₆H₃(H₂L^Me2)Cu(MeCN)] and (b) [Ph(H₂L^iPr2)-

Cu(MeCN)].

necessary to quantify the effect, this result confirms that the

O-isotope feature does mix with ligand vibrations and

provides support for this mixing as one rationale for the

complexity of the ¹⁶O₂resonance Raman data. Similar effects

have been noted for other bis(µ-oxo)dicopper compounds.^29b

Finally, we note the absence of any evidence for isomeric

(µ-η²:η²-peroxo)dicopper species in the Raman spectra,

consistent with the established tendency for systems sup-

ported by bidentated N-donor ligands to yield bis(µ-oxo)

compounds.^2e,3,4b,30

trum was obtained for the solution resulting from mixing

[Ph(H₂L^iPr2)CuCl]_xwith H₂O₂/NEt₃, proving that the same

bis(µ-oxo)dicopper complex formed in this alternative prepa-

ration. Single peaks also were observed for the systems

supported by H(Me₂L^Me2)^-and H(Me₂L^Et2)^-(Table 3, Figure

S4). For all other systems, two peaks of variable relative

intensity are observed in the spectra of the ¹⁶O₂-derived

intermediates, and these convert to a single peak when ¹⁸O₂

is used (cf. Figure 10a). With one exception, the difference

between the average of the two ¹⁶O₂bands and the single

¹⁸O₂peak falls in the range 25-30 cm^-1. The exception is

the system supported by 3,5-(CF₃)₂C₆H₃(H₂L^iPr2)^-, for which

the ¹⁶O₂bands are barely resolved and the difference between

the average and the ¹⁸O₂peak is ∼15 cm^-1(Figure S4).

The observation of multiple bands for only one oxygen

isotopomer (¹⁶O₂) suggests some type of vibrational mixing

of the [Cu₂(µ-O)₂]²⁺core mode either with an overtone or

combination band (Fermi resonance) or with a ligand-based

vibration, which disappears upon ¹⁸O-isotope shifting due

to a frequency mismatch. To investigate possible coupling

of ligand-based modes with the [Cu₂(µ-O)₂]²⁺core vibration,

we prepared [3,5-(CF₃)₂Ph(H₂L^CH3,CD3)Cu(MeCN)], in which

two of the four methyl groups (R′′) were perdeuterated. UV-

vis spectroscopic monitoring of the oxygenation of this

complex at -80 °C in THF revealed a spectrum identical to

that observed for the nondeuterated complex. An overlay of

resonance Raman spectra of the deuterated and parent system

(¹⁶O₂in Figure 11a; ¹⁸O₂in Figure 11b) shows shifts upon

ligand deuteration of bands at 467, 532, and 676 cm^-1that

are not O-isotope sensitive. Thus, these bands are clearly

associated with ligand-based vibrations, and their resonance

enhancement supports attribution of the intense ∼380 nm

absorption feature to a ligand-based π f π* transition.

Importantly, while the single band at 574 cm^-1in the ¹⁸O₂

spectrum is unperturbed within experimental error ((1 cm^-1)

by ligand deuteration (Figure 11b), the feature at 586 cm^-1

in the ¹⁶O₂spectrum of the parent system shifts by 6 cm^-1

upon deuterium substitution into the ligand methyl groups

(Figure 11a). Although more complete studies would be

Conclusion

The combined UV-vis, EPR, O₂uptake, and resonance

Raman data indicate that the â-diketiminate Cu(I) complexes

described herein react with O₂at low temperature to form

bis(µ-oxo)dicopper intermediates. These results contrast with

those reported previously for the Cu(I) complexes of

H(Me₂L^iPr2)^-and H(tBu₂L^iPr2)^-,⁹which yield monomeric 1:1

Cu/O₂adducts. This dichotomy may be rationalized by

invoking differences in effective steric bulk of the ligands

that are illustrated by the structural preferences of their Cu-

(II)-chloride compounds, [LCuCl]_n. The size of R′′ ³¹is one

basis for these effects, as revealed by the proclivity of

systems with R′′ ) Me or Et to yield dinuclear structures

[LCuCl]₂(which dissociate to some extent in solution) and

[L₂Cu₂(µ-O)₂]. The nature of the â-diketiminate backbone

substituents also underlies the steric effects, however, as

shown by the facts that (a) [Ph(H₂L^iPr2)CuCl]₂adopts a

dinuclear structure whereas H(Me₂L^iPr2)CuCl remains mono-

nuclear and (b) Cu(I) complexes of ligands with R ) aryl,

R′ ) H, and R′′ ) ⁱPr yield bis(µ-oxo)dicopper compounds

upon oxygenation. In these cases the effective steric bulk of

i

the R′′ ) Pr group is modulated by the â-diketiminate

backbone substituent pattern, whereby replacement of R′ )

Me with R′ ) H allows greater rotational flexibility of the

ⁱPr group (cf. structures in Figure 7a,b). This flexibility

(31) Related steric arguments have been presented to rationalize differences

in polymerization reactivity of â-diketiminate complexes of Zn(II);

see ref 14.

6316 Inorganic Chemistry, Vol. 41, No. 24, 2002

Copper Chemistry of â-Diketiminate Ligands

electrodes, a Ag wire reference electrode, and a BAS Epsilon

potentiostat connected to a cell mounted in a Vacuum Atmospheres

inert-atmosphere glovebox. All experiments were performed in

MeCN with 0.1 M Bu₄NPF₆at room temperature, and under these

conditions the ferrocene/ferrocenium E_1/2) +0.642 V vs Ag wire.

Elemental analyses were perfomed by Atlantic Microlab, Inc., or

Oneida Research Services, Inc. Mass spectra were recorded with a

JEOL JMS-700T tandem MS station, VG 7070-HF (FAB), or

Finnigan MAT 95 MS station.

Magnetic Measurements. The overall magnetic moment M of

[Cl(Me₂L^Me2)CuCl]₂was measured over the temperature range

5-300 K at four magnetic fields 0.5, 1, 2.5, and 5 T on a Quantum

Design MPMS superconducting quantum interference device

(SQUID) magnetometer. The sample (53 mg) was contained in a

Kel F bucket which had been independently calibrated. The data

were corrected for diamagnetism (-502 × 10^-6cm³mol^-1) using

Pascal’s constants.³³The low-field data were simulated using the

enables greater access to the Cu center, which can adopt a

4-coordinate geometry and form binuclear complexes with

single-atom bridges.

Experimental Section

General Considerations. All solvents and reagents were ob-

tained from commercial sources and used as received unless noted

otherwise. The solvents/reagents THF, pentane, CH₂Cl₂, toluene,

and benzene were distilled from Na/benzophenone or passed

through solvent purification columns (Glass Contour, Laguna, CA).

Heptanes, hexamethyldisiloxane (HMDSO), CH₃CN, and Et₃N were

n

distilled from CaH₂under nitrogen. The concentration of BuLi

was determined by titration with diphenylacetic acid in THF prior

to use. Labeled dioxygen (¹⁸O₂) was obtained from Cambridge

Isotopes, Inc., or Icon Isotopes, Inc. H₂¹⁸O₂was purchased from

Icon Isotopes, Inc., as a 2.7% solution in H₂O, with 90% ¹⁸O

enrichment. The compounds 2-methyl-6-perdeuteriomethylaniline,³²

2-phenyl-1,3-bis(dimethylamino)trimethinium hexafluorophos-

phate,¹⁶[NO₂(H₂L^Me2Me)H],¹²[CuCH₂SiMe₃]₄,²²and CuCl₂‚0.8THF¹⁸

were prepared as reported in the literature. All metal complexes

were synthesized and stored in a Vacuum Atmospheres inert-

atmosphere glovebox under a dry N₂atmosphere or by using

standard Schlenk and vacuum line techniques.

Van Vleck eq 1 derived from the Hamiltonian H ) -2JSˆ₁Sˆ₂

+

â_eHg˜Sˆ,³³with t being the temperature-independent paramagnetism

(TIP) and the other parameters assigned their usual meaning.

2

N_Aâ_e

M

ø_mT ≡ T ) 2

nH

1

g²

+ 2tT

(1)

k_BT

-2J

kT

3 + exp

(

)

Physical Methods. NMR spectra were recorded on a Varian

VI-300, VXR-300, JEOL FT-NMR Lambda 300WB, or Bruker

Advance 600 spectrometer. Chemical shifts (δ) for ¹H and ¹³C NMR

spectra were referenced to residual protium in the deuterated solvent.

UV-vis spectra were recorded on a HP8453 (190-1100 nm) diode

array spectrophotometer. Low-temperature spectra were acquired

using a custom-manufactured vacuum dewar equipped with quartz

windows, with low temperatures achieved with the use of a low-

temperature MeOH bath circulator or a Unisoku low-temperature

UV-vis cell holder. Samples for EPR spectroscopy were prepared

by bubbling O₂through a solution of the Cu(I) complex (≈2.0 mM)

at -80 °C in an EPR tube before freezing the solution in liquid

nitrogen or by adding 2 equiv of H₂O₂/Et₃N at -60 °C in an EPR

tube before incubating for 1 h and freezing the solution in liquid

nitrogen. X-band EPR spectra were recorded on a Bruker E-500

spectrometer, with an Oxford Insruments EPR-10 liquid-helium

cryostat (2-20 K, 9.61 GHz). Quantitation of EPR signal intensity

for copper complexes was accomplished by comparing the double

integration of the derivative spectrum to that of [H(Me₂L^iPr2)CuCl]^7a

in 1:1 CH₂Cl₂/toluene. The EPR simulation was performed using

the program EPR (F. Neese, University of Konstanz, Konstanz,

Germany). Samples for resonance Raman spectroscopy were

generated by bubbling ¹⁶O₂through a solution of the Cu(I) complex

(∼10 mM) at -80 °C, by freezing the solution at -196 °C and

transferring ca. 10 mL of ¹⁸O₂onto the solid and warming to -80

°C, or by adding 2 equiv of a 1:1 solution of 2.7% H₂O₂(in H₂O)

and Et₃N in THF. The starting complex concentrations were 10-

15 mM in THF, toluene, or MeCN. Resonance Raman spectra were

collected on an Acton 506 spectrometer using a Princeton Instru-

ments LN/CCD-1100-PB/UVAR detector and ST-1385 controller

interfaced with Winspec software. A Spectra-Physics 2030-15 argon

ion laser with a power of 200 mW at the sample was employed to

give the excitation at 457.9 nm. The spectra were obtained at -196

°C using a backscattering geometry; samples were placed in a

Teflon cup and frozen by direct immersion in liquid nitrogen.

Raman shifts were externally referenced to liquid indene. Cyclic

voltammetry was performed using Pt working and auxiliary

2-(3,5-Bis(trifluoromethyl))phenyl-1,3-bis(dimethylamino)-

trimethinium Hexafluorophosphate. 3,5-Bis(trifluoromethyl)-

phenylacetic acid (17.7 g, 65.2 mmol) was placed in a three-necked

round-bottomed flask, fitted with a dropping funnel and a reflux

condenser, and purged with N₂. DMF (29 mL, 391 mmol) was

added to the flask via syringe, and the solution was warmed to 70

°C. POCl₃(10.0 g, 65.2 mmol) was placed in the dropping funnel

and was added to the reaction mixture over approximately 2 h.

After addition the crimson solution was heated at 70 °C for a further

3 h before being cooled to ambient temperature. A NaOH solution

(35 mL of 5 M) and the reaction mixture were slowly and

simultaneously added to a solution of HPF₆(17.1 g, 10.4 mL, 60

wt % solution in H₂O), 5 M NaOH (18 mL), and H₂O (75 mL),

while cooling in an ice bath and keeping T < 10 °C. After addition

the solution was allowed to age for ca. 1 h while a yellow precipitate

formed. The solution was filtered under vacuum, yielding a yellow

solid. The solid was dissolved in the minimum of hot MeCN and

filtered under vacuum. Excess Et₂O was added to the MeCN

solution, which was placed at -20 °C overnight. Filtration of the

solution under gravity yielded a yellow crystalline solid (13.4 g,

43%): ¹H NMR (CD₃CN, 300 MHz) δ 8.06 (s, 1H), 7.91 (s,

2H), 7.44 (s, 2H), 3.25 (s, 6H), 2.41 (s, 6H) ppm; ¹³C{¹H} NMR

(CD₃CN, 75 MHz) δ 164.23, 133.81, 132.30 (quartet, J ) 271 Hz),

133.81, 124.41 (quartet, J ) 33.8 Hz), 123.87, 103.11, 49.99, 41.47

ppm; FAB MS m/z 339.1301 ([M - PF₆]). Anal. Calcd for

C₁₅H₁₇N₂PF₁₂: C, 37.19; H, 3.51; N, 5.79. Found: C, 36.89; H,

3.37; N, 5.72.

General Method for the Preparation of â-Diketimines.¹⁶The

appropriate vinamidinium salt (typically 5 g, 13.2 mmol) was

dissolved in EtOH (30 mL) and aqueous NaOH (30 mL of 25 wt

%) and brought to reflux for approximately 45 min. After being

cooled to ambient temperature, the biphasic solution was brought

to pH 1 by the addition of 4 M HCl and extracted with Et₂O (2 ×

100 mL). The organic fractions were combined, dried over MgSO₄,

and filtered, and the solvent was removed under vacuum to yield

a brown oil, which was used without further purification. A

(32) Eibler, E.; Ka¨sbauer, J.; Pohl, H.; Sauer, J. Tetrahedron Lett. 1987,

28, 1097-1100.

(33) Kahn, O. Molecular Magnetism; VCH: New York, 1993.

Inorganic Chemistry, Vol. 41, No. 24, 2002 6317

Spencer et al.

quantitative yield for the hydrolysis was assumed for the â-diketimine

syntheses. The brown oil was dissolved in EtOH (50 mL), and the

desired aniline derivative (2.1 equiv) was added dropwise with 12

M HCl (1 equiv). The resulting solution was brought to reflux for

approximately 1 h, cooled to ambient temperature, and then stirred

overnight. The resulting brown solution was neutralized by the

addition of excess NaHCO₃and extracted with CHCl₃(3 × 100

mL). The organic fractions were combined, dried over MgSO₄, and

filtered, and the solvent was removed under vacuum to yield a

brown oil. Recrystallization from MeOH yielded the product as a

yellow crystalline solid in the indicated yield.

19.21 ppm. FAB MS: m/z 491.1932 ([M + H]⁺). Anal. Calcd for

C₂₇H₂₄N₂F₆: C, 66.12; H, 4.90; N, 5.71. Found: C, 65.93; H, 5.01;

N, 5.69.

1-(2-Methyl-6-trideuteriomethylphenyl)amino-3-(2-methyl-

6-trideuteriomethylphenyl)imino-2-(3,5-bis(trifluoromethyl))-

phenyl-1-propene, [3,5-(CF₃)₂C₆H₃(H₂L^CH3,CD3)H]. Yield: 18%.

¹H NMR (C₆D₆, 300 MHz): δ 12.38 (br. s, 1H), 7.64 (s, 1H), 7.52

(s, 2H), 7.38 (s, 2H), 6.99 (s, 6H), 2.12 (s, 3H) ppm. ¹³C{¹H} NMR

(C₆D₆, 75 Mz): δ 155.21, 145.77, 143.45, 132.50 (quartet, J ) 32

Hz), 130.62, 130.51, 129.30, 125.63, 125.50, 124.45 (quartet, J )

272 Hz), 118.78, 105.13, 19.18, 18.65 (heptet, J ) 20 Hz). EI MS:

m/z 496.2190 (M⁺). Anal. Calcd for C₂₇H₁₈D₆F₆N₂: C, 65.32; H,

4.83; N, 5.65. Found: C, 65.10; H, 4.79; N, 5.56.

1-(2,6-Diisopropylphenyl)amino-3-(2,6-diisopropylphenyl)-

imino-2-phenyl-1 -propene [Ph(H₂L^iPr2)H]. Yield: 50%. ¹H NMR

(C₆D₆, 300 MHz): δ 12.45 (br s, 1H), 7.05-7.82 (m, 11H), 7.73

(s, 2H), 3.45 (heptet, J ) 6.9 Hz, 4H), 1.21 (d, J ) 6.9 Hz, 12H)

ppm. ¹³C{¹H} NMR (C₆D₆, 75 MHz): δ 156.20, 144.40, 142.26,

140.82, 126.40, 125.78, 125.53, 124.11, 107.01 ppm. FAB MS:

m/z 467.3414 ([M + H]⁺). Anal. Calcd for C₃₃H₄₂N₂: C, 84.98;

H, 9.01; N, 6.0. Found: C, 84.96; H, 9.23; N, 5.92.

2-(2,6-Dimethylphenyl)amino)-4-((2,6-dimethylphenyl)imino-

3-chloro-2-pentene, [Cl(Me₂L^Me)H]. A 500 mL round-bottom flask

was charged with a solution of 3-chloropentanedione (10.5 g, 78.3

mmol), 2,6-dimethylaniline (19.0 g, 157 mmol), and a catalytic

amount of p-toluenesulfonic acid hydrate (approximately 0.50 g)

in toluene (250 mL). The flask was equipped with a Dean-Stark

apparatus, and the reaction mixture was refluxed under N₂for 24

h, resulting in the development of a dark brown color. After the

mixture was cooled to ambient temperature, the volatiles were

removed under reduced pressure, yielding a dark brown oil. MeOH

(150 mL) was added, yielding a suspension that was stirred for 30

min. The suspension was filtered to yield a tan powder, which was

washed with cold MeOH (2 × 100 mL) and dried in vacuo.

Recrystallization from the minimum amount of warm pentane

yielded the product as tan crystals (2.18 g, 8.2%). ¹H NMR (C₆D₆,

300 MHz): δ 12.95 (br s, 1H), 6.94 (s, 6H), 2.02 (s, 12H), 1.90 (s,

6H) ppm. ¹³C{¹H} NMR (C₆D₆, 75 MHz): δ 160.8, 144.0, 132.6,

128.7, 125.5, 19.0, 18.8 ppm. LREIMS: m/z ) 340 (M⁺). Anal.

Calcd for C₂₁H₂₅N₂Cl: C, 73.99; H, 7.39; N, 8.22. Found: C, 74.17;

H, 7.42; N 8.21.

1-(2,6-Diethylphenyl)amino-3-(2,6-diethylphenyl)imino-2-phen-

1

yl-1-propene [Ph(H₂L^Et2)H]. Yield: 25%. H NMR (C₆D₆, 300

MHz): δ 12.73 (br s, 1H), 7.84 (s, 2H), 7.31 (m, 5H), 7.16 (m,

6H), 2.77 (q, J ) 7.5 Hz, 8H), 1.25 (t, J ) 7.5 Hz, 12H) ppm.

¹³C{¹H} NMR (C₆D₆, 75 MHz): δ 155.75, 145.63, 140.93, 137.41,

129.36, 127.44, 125.97, 125.84, 125.52, 107.28, 25.94, 15.61 ppm.

FAB MS: m/z 411.2786 ([M + H]⁺). Anal. Calcd for C₂₉H₃₄N₂:

C, 84.88; H, 8.29; N, 6.83. Found: C, 84.94; H, 8.35; N, 6.78.

1-(2,6-Dimethylphenyl)amino-3-(2,6-dimethylphenyl)imino-

2-phenyl-1-propene [Ph(H₂L^Me2)H]. Yield: 33%. ¹H NMR (C₆D₆,

300 MHz): δ 12.04 (br s, 1H), 7.64 (s, 2H), 7.16 (m, 7H), 6.95

(m, 4H), 2.18 (s, 12H) ppm. ¹³C{¹H} NMR (C₆D₆, 75 MHz): δ

155.25, 146.60, 141.01, 130.62, 129.30, 129.17, 126.16, 125.55,

125.04, 107.53, 19.37 ppm. FAB MS: m/z 355.2163 ([M + H]⁺).

Anal. Calcd for C₂₅H₂₆N₂: C, 84.75; H, 7.34; N, 7.91. Found: C,

84.43; H, 7.36; N, 7.88.

n

[Ph(H₂L^iPr2)Li‚THF]. In an inert atmosphere BuLi (0.43 mL,

1.0 equiv, 2.5 M in hexanes) was added dropwise to a stirred

solution of [Ph(H₂L^iPr2)H] (0.50 g, 1.07 mmol) in THF (5 mL).

The golden yellow solution was stirred for approximately 30 min

and the solvent removed under vacuum. The residue was dissolved

in pentane (ca. 20 mL) and left at -20 °C overnight. Yellow crystals

deposited, which were washed with cold pentane and dried in vacuo

1-(2,6-Diisopropylphenyl)amino-3-(2,6-diisopropylphen-

yl)imino-2-(3,5-bis(trifluoromethyl))phenyl-1-propene [3,5-(CF₃)₂-

C₆H₃(H₂L^iPr2)H]. Yield: 20%. ¹H NMR (C₆D₆, 300 MHz): δ 12.74

(br. s, 1H), 7.67 (m, 3H), 7.65 (s, 2H), 7.14 (m, 6H), 3.38 (heptet,

J ) 6.9 Hz, 4H), 1.22 (d, J ) 6.9 Hz, 24H) ppm. ¹³C{¹H} NMR

(C₆D₆, 75 MHz): δ 156.18, 143.31, 143.60, 143.31, 142.04, 132.76

(quartet, J ) 32.6 Hz), 125.13, 124.42 (quartet, J ) 270.9 Hz),

124.33, 118.76, 104.84, 29.21, 24.19 ppm. FAB MS: m/z 603.3182

([M + H]⁺). Anal. Calcd for C₃₅H₄₀N₂F₆: C, 69.77; H, 6.64; N,

4.65. Found: C, 69.71; H, 6.79; N, 4.66.

1

(0.463 g, 79%). H NMR (C₆D₆, 300 MHz): δ 8.11 (s, 2H), 7.50

(m, 2H), 7.19 (m, 8H), 7.01 (m, 1H), 3.51 (heptet, J ) 6.9 Hz,

4H), 3.26 (m, 4H), 1.23 (d, J ) 6.9 Hz, 24H), 1.16 (m, 4H) ppm.

¹³C{¹H} NMR (C₆D₆, 75 MHz): δ 161.80, 152.76, 145.72, 141.81,

129.08, 125.98, 124.24, 123.77, 123.26, 104.71, 68.45, 28.79, 25.10,

25.71, 23.99 ppm.

n

[Ph(H₂L^Et2)Li]. In an inert atmosphere BuLi (0.34 mL, 1.0

1-(2,6-Diethylphenyl)amino-3-(2,6-diethylphenyl)imino-2-(3,5-

bis(trifluoromethyl))phenyl-1-propene [3,5-(CF₃)₂C₆H₃(H₂L^Et2)H].

Yield: 25%. ¹H NMR (C₆D₆, 300 MHz): δ 12.70 (br. s, 1H), 7.77

(s, 2H), 7.68 (s, 1H), 7.32 (s, 2H), 7.18 (m, 6H), 2.73 (quartet, J )

7.5 Hz, 8H), 1.28 (t, J ) 7.5 Hz, 12H) ppm. ¹³C{¹H} NMR (C₆D₆,

75 MHz): δ 155.65, 144.75, 143.37, 132.58 (quartet, J ) 32.4

Hz), 124.45 (quartet, J ) 271.1 Hz), 123.33, 127.60, 126.34, 125.7,

118.75, 104.96, 25.79, 15.62 ppm. FAB MS: m/z 547.2567 ([M +

H]⁺). Anal. Calcd for C₃₁H₃₂N₂F₆: C, 68.13; H, 5.86; N, 5.13.

Found: C, 68.01; H, 5.86; N, 5.07.

equiv, 2.5 M in hexanes) was added dropwise to a stirred solution

of [Ph(H₂L^Et2)H] (0.35 g, 0.85 mmol) in pentane (5 mL). The

solution was stirred for approximately 30 min with the production

of a cream precipitate. The solution was reduced in volume and

was placed at -20 °C overnight. The solution was filtered under

vacuum yielding a cream solid (0.33 g, 93%). ¹H NMR (C₆D₆, 300

MHz): δ 7.85 (s, 2H), 7.36 (m, 2H), 7.17 (m, 8H), 7.03 (m, 1H),

2.50 (quartet, J ) 7.5 Hz, 8H), 1.18 (t, J ) 7.5 Hz, 12H) ppm.

¹³C{¹H} NMR (C₆D₆, 75 MHz): δ 161.16, 153.84, 145.30, 137.25,

128.99, 126.83, 125.83, 123.99, 123.34, 104.53, 26.05, 15.74 ppm.

1-(2,6-Dimethylphenyl)amino-3-(2,6-dimethylphenyl)imino-

2-(3,5-bis(trifluoromethyl))phenyl-1-propene [3,5-(CF₃)₂C₆H₃-

n

[Ph(H₂L^Me2)Li‚THF]. In an inert atmosphere BuLi (0.50 mL,

1

(H₂L^Me2)H]. Yield: 28%. H NMR (C₆D₆, 300 MHz): δ 12.36

1.0 equiv, 2.5 M in hexanes) was added dropwise to a stirred

solution of [Ph(H₂L^Me2)H] (0.44 g, 1.24 mmol) in THF (5 mL).

The solution was stirred for approximately 30 min and reduced in

volume. A large excess of pentane was added, and the solution

was placed at -20 °C overnight. The mother liquor was decanted

(br s, 1H), 7.63 (s, 1H), 7.51 (s, 2H), 7.37 (s, 2H), 6.94 (m, 6H),

2.11 (s, 12H) ppm. ¹³C{¹H} NMR (C₆D₆, 75 MHz): δ 155.22,

145.74, 143.44, 132.49 (quartet, J ) 32.4 Hz), 130.63, 129.29,

125.63, 124.46 (quartet, J ) 271.1 Hz), 125.51, 118.78, 105.13,

6318 Inorganic Chemistry, Vol. 41, No. 24, 2002

Copper Chemistry of â-Diketiminate Ligands

1

away from the brown crystals, which were washed with cold

pentane and dried under vacuum (0.39 g, 73%). H NMR (C₆D₆,

300 MHz): δ 8.09 (s, 2H), 700-7.49 (m, 11H), 3.29 (m, 4H),

2.34 (s, 12H), 1.18 (m, 4H) ppm. ¹³C{¹H} NMR (C₆D₆, 75 MHz):

δ 161.35, 155.46, 145.93, 130.80, 128.99, 128.89, 125.95, 123.07,

123.07, 105.07, 68.30, 25.71, 19.63 ppm.

crystals (total yield ) 0.35 g, 57%). H NMR (C₆D₆, 300 MHz):

1

δ 7.04 (d, 4H), 6.88 (t, 2H), 3.06-3.10 (m, 6H), 2.26 (s, 6H), 2.15

(s, 12H), 1.07-1.12 (m, 6H) ppm. ¹³C{¹H} NMR (C₆D₆, 75

MHz): δ 162.46, 152.47, 130.95, 128.53, 122.48, 68.10, 25.66,

21.76, 19.25 ppm.

[Cl(Me₂L^Me2)CuCl]₂. A solution of [Cl(Me₂L^Me2)]Li‚1.5 THF

(0.512 g, 1.22 mmol) in THF (6 mL) was added to a slurry of

CuCl₂‚0.8 THF (0.235 g, 1.22 mmol) in THF (6 mL), causing the

formation of a dark green color. The reaction mixture was stirred

overnight, and the solvent was removed under reduced pressure.

The green residue was extracted with CH₂Cl₂(10 mL), yielding a

purple solution that was filtered through a pad of Celite. The volume

of solvent was reduced to 5 mL, HMDSO (5 mL) was added, and

the solution was stored at -20 °C overnight, causing the deposition

of dark crystals. The volume of the mother liquor was reduced and

the solution stored at -20 °C, resulting in the formation of a second

crop of crystals (total yield ) 0.287 g, 54%). UV-vis (CH₂Cl₂)

[λ_max, nm (ꢀ, M^-1cm^-1)]: 283 (5900), 327 (11 500), 362 (14 400),

505 (2500), 812 (600). Anal. Calcd for C₄₂H₄₈N₄Cu₂Cl₂: C, 57.47;

H, 5.51; N, 6.38. Found: C, 57.56; H, 5.52; N, 6.36.

[H(Me₂L^Et2)CuCl]₂. A solution of H(Me₂L^Et)Li (0.390 g, 1.06

mmol) in THF (5 mL) was added to a slurry of CuCl₂‚0.8THF

(0.203 g, 1.06 mmol) in THF (5 mL), causing the development of

a green-brown color. Manipulation as in the preparation of

[Cl(Me₂L^Me2)CuCl]₂afforded the product as dark crystals (total yield

) 0.255 g, 52%). UV-vis (CH₂Cl₂) [λ_max, nm (ꢀ, M^-1cm^-1)]:

283 (9800), 325 (15 100), 339 (13 800), 508 (3200), 640 (sh 800),

831 (500). Anal. Calcd for C₅₀H₆₆Cu₂N₄Cl₂: C, 65.20; H, 7.22; N,

6.08. Found: C, 64.87; H, 7.23; N, 6.01.

[Ph(H₂L^iPr2)CuCl]₂. A solution of [Ph(H₂L^iPr2)Li‚THF] (0.176

g, 0.323 mmol) in THF (4 mL) was added to a slurry of CuCl₂‚

0.8THF (0.062 g, 0.323 mmol) in THF (4 mL), causing the

development of a dark green color. The reaction mixture was stirred

for 5 h, and the volatiles were removed under reduced pressure.

The green residue was extracted with 6 mL of CH₂Cl₂, forming a

deep brown-red solution that was filtered through a pad of Celite.

The volume was reduced to 4 mL, and 2 mL of heptanes was added.

Storage at -20 °C resulted in the deposition of green crystals.

Addition of 2 mL of HMDSO to the mother liquor followed by

cooling led to the formation of a second crop of crystals (total yield

) 0.062 g, 34%). UV-vis (CH₂Cl₂) [λ_max, nm (ꢀ, M^-1cm^-1)]:

283 (21 100), 327 (8400), 379 (17 800), 514 (3000), 664 (sh, 1000),

837 (660). Anal. Calcd for C₆₆H₈₂N₄Cu₂Cl₂: C, 70.19; H, 7.32, N

4.96. Found: C, 70.39; H, 7.35; N, 4.99.

General Method for the Preparation of Cu(I) Complexes. In

an inert atmosphere a solution of â-diketiminate lithium salt

(0.1-1.0 mmol) in THF (2 mL) was added to a slurry of

[Cu(MeCN)₄]CF₃SO₃(1.0 equiv) in THF and stirred for 5 min.

The solvent was removed under vacuum and the residue extracted

with pentane (between 10 and 25 mL depending on complex

formed) and filtered through a plug of Celite. The volume was

reduced and the solution was placed at -20 °C overnight, yielding

a yellow powder. The mother liquor was decanted away from the

solid, which was dried under vacuum.

[3,5-(CF₃)₂C₆H₃(H₂Li^Pr2)Li]. In an inert atmosphere ⁿBuLi (0.33

mL, 1.0 equiv, 2.5 M in hexanes) was added dropwise to a stirred

solution of [3,5-(CF₃)₂C₆H₃(H₂L^iPr2)H] (0.50 g, 0.83 mmol) in

pentane (5 mL). The solution was stirred for approximately 30 min,

with the production of a cream precipitate, reduced in volume, and

placed at -20 °C overnight. The solution was filtered under vacuum

1

to give a cream solid (0.44 g, 87%). H NMR (C₆D₆, 300 MHz):

δ 7.84 (s, 2H), 7.80 (s, 2H), 7.48 (s, 1H), 7.16 (m, 6H), 2.95 (heptet,

J ) 6.9 Hz, 4H), 1.15 (dd, J ) 6.9 Hz, 24H) ppm. ¹³C{¹H} NMR

(C₆D₆, 75 MHz): δ 161.49, 151.34, 147.73, 141.31, 132.36 (quartet,

J ) 32.1 Hz), 125.04, 124.79 (quartet, J ) 271.4 Hz), 124.43,

123.96, 116.16, 104.84, 28.93, 25.83, 23.29 ppm.

[3,5-(CF₃)₂C₆H₃(H₂L^Et2)Li]. In an inert atmosphere ⁿBuLi (0.22

mL, 1.0 equiv, 2.5 M in hexanes) was added dropwise to a stirred

solution of [3,5-(CF₃)₂C₆H₃(H₂L^Et2)H] (0.30 g, 0.55 mmol) in

pentane (5 mL). The solution was stirred for approximately 30 min,

with the production of a cream precipitate, reduced in volume, and

placed at -20 °C overnight. The solution was filtered under vacuum

1

to give a cream solid (0.27 g, 89%). H NMR (C₆D₆, 300 MHz):

δ 7.84 (s, 2H), 7.82 (s, 2H), 7.56 (s, 1H), 7.16-7.24 (m, 6H), 2.44

(quartet, J ) 7.5 Hz, 8H), 1.18 (t, J ) 7.5 Hz, 12H) ppm. ¹³C{¹H}

NMR (C₆D₆, 75 MHz): δ 161.01, 152.58, 147.71, 136.68, 132.25

(quartet, J ) 31.6 Hz), 127.10, 126.34, 124.80 (quartet, J ) 271.4

Hz), 124.57, 116.14 102.75, 25.89, 15.75 ppm.

[3,5-(CF₃)₂C₆H₃(H₂L^Me2)Li]. In an inert atmosphere ⁿBuLi (0.24

mL, 1.0 equiv, 2.5 M in hexanes) was added dropwise to a stirred

solution of [3,5-(CF₃)₂C₆H₃(H₂L^Me2)H] (0.30 g, 0.61 mmol) in

pentane (5 mL). The solution was stirred for approximately 30 min,

with the production of a pale yellow precipitate, reduced in volume,

and placed at -20 °C. The solution was filtered under vacuum to

give a pale yellow solid (0.29 g, 96%). ¹H NMR (C₆D₆, 300

MHz): δ 7.74 (s, 2H), 7.73 (s, 2H), 7.60 (s, 1H), 7.07-7.28 (m,

6H), 2.09 (s, 12H) ppm. ¹³C{¹H} NMR (C₆D₆, 75 MHz): δ 160.60,

153.60, 147.66, 132.07 (quartet, J ) 32.1 Hz), 130.42, 129.30,

124.82 (quartet, J ) 271 Hz), 124.87, 124.04, 116.45, 103.42, 19.37

ppm.

[3,5-(CF₃)₂C₆H₃(H₂L^CH3,CD3)Li]. In an inert atmosphere ⁿBuLi

(0.29 mL, 1.2 equiv, 2.5 M in hexanes) was added dropwise to a

stirred solution of [3,5-(CF₃)₂C₆H₃(H₂L^CH3,CD3)H] (0.30 g, 0.60

mmol) in pentane (5 mL). The solution was stirred for ap-

proximately 30 min, with the production of a pale yellow precipitate,

reduced in volume, and placed at -20 °C. The solution was filtered

under vacuum to give a pale yellow solid (0.23 g, 74%). ¹H NMR

(C₆D₆, 300 MHz): δ 7.64 (s, 4H), 7.49 (s, 1H), 7.00 (m, 6H), 2.00

(s, 3H) ppm. ¹³C{¹H} NMR (C₆D₆, 75 MHz): δ 160.69, 153.68,

147.70, 132.08 (quartet, J ) 32.1 Hz), 130.40, 130.28, 128.98,

124.86, 124.83 (quartet, J ) 271 Hz), 124.02, 116.15, 103.43, 19.39

ppm.

[H(Me₂L^Et2)Cu(MeCN)]. This complex was isolated from

pentane at -20 °C to give a yellow powder (57%). Drying under

vacuum resulted in the loss of coordinated MeCN. ¹H NMR (C₆D₆,

300 MHz): δ 7.15 (m, 6H), 4.82 (s, 1H), 2.46 (q, J ) 7.5 Hz,

8H), 1.70 (s, 6H), 1.15 (t, J ) 7.5 Hz, 12H) ppm. Anal. Calcd for

C₂₅H₃₃N₂Cu: C, 70.67; H, 7.77; N, 6.60. Found: C, 71.41; H, 7.64;

N, 7.20.

[Cl(Me₂L^Me2)]Li‚1.5THF. A solution of n-butyllithium (0.60

mL, 2.57 M in hexanes) was slowly added to a solution of

[Cl(Me₂L^Me2)H] (0.50 g, 1.47 mmol) in THF (5 mL). After the

resulting brown solution was stirrred for 30 min, the volume was

decreased to 2 mL under reduced pressure. Pentane (4 mL) was

added, and the solution was stored at -20 °C overnight. Yellow

crystals formed, which were washed with cold pentane (1 × 2 mL)

and dried in vacuo. The supernatant was further concentrated and

stored at -20 °C, resulting in the formation of a second crop of

[H(Me₂L^Me2)Cu(MeCN)]. This complex was isolated from

pentane at -20 °C to give a yellow powder (40%). Drying under

Inorganic Chemistry, Vol. 41, No. 24, 2002 6319

Spencer et al.

vacuum resulted in the loss of coordinated MeCN. ¹H NMR (C₆D₆,

300 MHz): δ 7.13 (m, 4H), 6.99 (m, 2H), 4.79 (s, 1H), 2.03 (s,

12H), 1.65 (s, 6H) ppm. Anal. Calcd for C₂₅H₃₃N₂Cu: C, 68.39;

H, 6.78; N, 7.60. Found: C, 68.96; H, 7.07; N, 7.28.

MHz): δ 162.7, 153.2, 135.4, 130.4, 129.0, 128.8, 127.9, 123.3,

102.7, 21.5, 19.7, 18.4 ppm. UV-vis (THF) [λ_max, nm (ꢀ, M^-1

cm^-1): 359 (25 000). FTIR (KBr, cm^-1): 2128 (ν_CN). Anal. Calcd

for C₃₀H₃₃N₃ClCu: C, 67.40; H, 6.22; N, 7.86. Found: C, 67.55;

H, 6.43; N, 7.58.

[Ph(H₂L^iPr2)Cu(MeCN)]. This complex was recrystallized from

1

[{NO₂(H₂L^Me2Me)Cu}₂(µ-OH)₂]. An anaerobic MeCN solution

(10 mL) containing [NO₂(H₂L^Me2Me)Cu(MeCN)] (41 mg, 0.1 mmol

based on cuprous ion) was prepared by dissolving the polymer

[NO₂(H₂L^Me2Me)Cu]_x.¹²Dry O₂was introduced into the solution by

bubbling it through a needle at -40 °C for several min. The color

of the solution turned from pale yellow to dark brown. The solution

was allowed to stand for several h at -40 °C and then warmed to

room temperature. Removal of the solvent by evaporation gave a

residue, which was recrystallized from CH₂Cl₂to give the product

(38 mg, 87%). UV-vis (MeCN) [λ_max, nm (ꢀ, M^-1cm^-1)]: 353

(33 100). FTIR (KBr, cm^-1): 3638, 1613, 1601, 1530, 1296. Anal.

Calcd for C₄₂H₅₀N₆O₆Cu₂: C, 58.52; H, 5.85; N, 9.75. Found: C,

58.27; H, 5.82; N, 9.62.

pentane at -20 °C to give a yellow crystalline solid (60%). H

NMR (C₆D₆, 300 MHz): δ 8.00 (s, 2H), 7.36 (d, J ) 7.5 Hz, 8H),

7.15 (m, 8H), 7.00 (t, J ) 7.5 Hz, 1H), 3.34 (heptet, J ) 6.9 Hz,

4H), 1.18 (d, J ) 6.9 Hz, 12H), 1.05 (d, J ) 6.9 Hz, 12H), 0.27 (s,

3H) ppm. Anal. Calcd for C₃₅H₄₄N₃Cu: C, 73.71; H, 7.54; N, 7.39.

Found: C, 73.71; H, 7.78; N, 7.37.

[Ph(H₂L^Et2)Cu(MeCN)]. This complex was isolated from pen-

tane at -20 °C to give a yellow powder (51%). Drying under

vacuum resulted in the loss of coordinated MeCN. ¹H NMR (C₆D₆,

300 MHz): δ 7.94 (s, 2H), 7.04-7.31 (m, 11H), 2.56 (m, 8H),

1.15 (t, J ) 7.5 Hz, 12H) ppm. Anal. Calcd for C₂₉H₃₃N₂Cu: C,

73.62; H, 7.03; H, 5.92. Found: C, 73.76; H, 6.99; N, 5.89.

[Ph(H₂L^Me2)Cu(MeCN)]. This complex was isolated from

pentane at -20 °C to give a yellow powder (31%). Drying under

vacuum resulted in the loss of coordinated MeCN. ¹H NMR (C₆D₆,

300 MHz): δ 7.81 (s, 2H), 7.02-7.19 (m, 11H), 2.09 (s, 12H)

ppm. Anal. Calcd for C₂₅H₂₅N₂Cu: C, 72.00; H, 6.04; N, 6.71.

Found: C, 72.02; H, 6.00; N, 6.72.

Spectrophotometric O₂Titrations. A 4 mL sample of a stock

solution of [Ph(H₂L^iPr2)Cu(MeCN)] in THF (0.25 mM) was placed

in a UV-vis cuvette and cooled to -80 °C, and the headspace of

the cuvette was evacuated. Spectra were taken before and after to

ensure that no sample degradation had occurred. Using a syringe,

either 1.0, 0.75, 0.5, or 0.25 equiv of O₂(by volume of 1% O₂in

N₂gas) was injected into the cuvette where it was left to equilibrate,

with occasional mild agitation. The progress of oxygenation was

followed by monitoring the shoulder at 433 nm in the UV-vis

spectrum. In each case, the reaction was run until no further increase

in absorbance at 433 nm was observed. Measured absorbance values

of 1.09, 1.08, 1.01, and 0.69, respectively, were consistent with a

Cu:O₂stoichiometry of 2.0(2):1.

[3,5-(CF₃)₂C₆H₃(H₂L^iPr2)Cu(MeCN)]. This complex was re-

crystallized from pentane at -20 °C to give a yellow crystalline

1

solid (55%). H NMR (C₆D₆, 300 MHz): δ 8.01 (s, 2H), 7.84 (s,

2H), 7.52 (s, 1H), 7.17 (m, 6H), 3.50 (heptet, J ) 6.9 Hz, 4H),

1.29 (d, J ) 6.9 Hz, 12H), 1.19 (d, J ) 6.9 Hz, 12H), 0.20 (s, 3H)

ppm. Anal. Calcd for C₃₇H₄₂N₃F₆Cu: C, 62.93; H, 5.95; N, 5.95.

Found: C, 62.87; H, 6.05; N, 5.91.

[3,5-(CF₃)₂C₆H₃(H₂L^Et2)Cu(MeCN)]. This complex was isolated

from pentane at -20 °C to give a yellow powder (56%). Drying

under vacuum resulted in partial loss of MeCN (0.3 equiv

X-ray Crystallography. Crystal data and collection param-

eters are listed in Table 2. A crystal of the appropriate size (with

one exception; see Supporting Information for full information in

the form of CIFs) was mounted on a glass fiber using fluorinated

oil and transferred to either a Siemens or Bruker SMART

diffractometer/CCD area detector or a Rigaku RAXIS-RAPID

imaging plate two-dimensional area detector. The crystal was

centered in the X-ray beam (Mo KR radiation; λ ) 0.710 73 Å,

graphite monochromator) for data collection. The intensity data were

corrected for Lorentz polarization effects (SAINT)³⁴and absorption

[SADABS,³⁵XPREP,³⁶or the crystal structure software from the

Molecular Structure Corp. (CSS-MSC)³⁷]. The structure was solved

by direct methods using SHELXS-97,³⁸SIR92,³⁹or CSS-MSC,³⁷

which provided most non-hydrogen atoms. Full-matrix least-

squares/difference Fourier cycles were performed using SHELXL-

97,³⁸which located the remaining non-hydrogen atoms. All non-

hydrogen atoms were refined with anisotropic displacement

parameters. All hydrogen atoms were placed in ideal positions and

refined as riding atoms with isotropic displacement parameters

related to the parent atom. Pertinent details for each structure are

noted below; see Supporting Information for full information in

the form of CIFs.

1

remaining). H NMR (C₆D₆, 300 MHz): δ 7.92 (s, 2H), 7.80 (s,

2H), 7.60 (m, 1H), 7.19-7.23 (m, 6H), 2.60 (m, 8H), 1.21 (t, J )

7.5 Hz, 12H), 0.37 (s, 1H) ppm. Anal. Calcd for C₃₁H₃₁N₂F₆Cu‚

1/3CH₃CN: C, 61.08; H, 5.14; N, 5.25. Found: C, 61.16; H, 5.03;

N, 5.17.

[3,5-(CF₃)₂C₆H₃(H₂L^Me2)Cu(MeCN)]. This complex was iso-

lated from pentane at -20 °C to give a yellow powder (25%).

1

Drying under vacuum resulted in loss of MeCN. H NMR (C₆D₆,

300 MHz): δ 7.78 (s, 2H), 7.70 (s, 2H), 7.65 (s, 1H), 7.08-7.28

(m, 6H), 2.17 (s, 12H) ppm. Anal. Calcd for C₂₇H₂₃N₂F₆Cu: C,

58.64; H, 4.19; N, 5.07. Found: C, 59.12; H, 4.11; N, 4.95.

[3,5-(CF₃)₂C₆H₃(H₂L^CH3,CD3)Cu(MeCN)]. This complex was

isolated from pentane at -20 °C to give a yellow powder (46%).

1

Drying under vacuum resulted in loss of MeCN. H NMR (C₆D₆,

300 MHz): δ 7.63 (s, 2H), 7.56 (s, 2H), 7.53 (s, 1H), 7.02 (m,

6H), 2.00 (s, 6H) ppm. Anal. Calcd for C₂₇H₂₃N₂F₆D₆Cu: C, 58.01;

H, 4.12; N, 5.01. Found: C, 57.75; H, 3.99; N, 4.84.

[Cl(Me₂L^Me2)Cu(CNC₆H₃Me₂)]. A solution of Cl(Me₂L^Me2)H

(0.200 g, 0.587 mmol) in THF (10 mL) was treated with [CuCH₂-

SiMe₃]₄(0.088 g, 0.587 mmol) and 2,6-dimethylphenyl 1-isocyanide

(0.077 g, 0.587 mmol), causing the formation of a yellow solution.

The reaction mixture was stirred for 30 min, and the solvent was

removed in vacuo to yield a light brown solid. This solid was taken

up in Et₂O (15 mL), the solution was filtered, and the solvent

volume was reduced to 10 mL. Storage of the filtrate at -20 °C

overnight led to the deposition of light yellow crystals that were

isolated and dried under reduced pressure (0.132 g, 42%). ¹H NMR

(C₆D₆, 300 MHz): δ 7.05 (d, J ) 7.5 Hz, 4H), 6.92 (t, J ) 7.5 Hz,

2H), 6.58 (t, J ) 7.5 Hz, 1H), 6.37 (d, J ) 7.5 Hz, 2H), 2.31 (s,

12H), 2.21 (s, 6H), 1.57 (s, 6H) ppm. ¹³C{¹H} NMR (C₆D₆, 75

(34) SAINT V6.01; Bruker Analytical X-ray Systems: Madison, WI, 1999.

(35) An empirical correction for absorption anisotropy: Blessing, R. Acta

Crystallogr. 1995, A51, 33-38.

(36) Bruker Data Preparation & Reciprocal Space Exploration, ver. 5.1;

Bruker-AXS, Inc.: Madison, WI, 1997.

(37) Crystal Structure Analysis Package, version 2.0; Molecular Structure

Corp. and Rigaku Corp: The Woodlands, TX, 2001.

(38) SHELXTL-Plus, V5.10, Bruker Analytical X-ray Systems: Madison,

WI, 1997.

(39) Altomare, A.; Cascarno, G.; Giacovazzo, C.; Gualardi, A. SIR92. J.

Appl. Crystallogr. 1993, 26, 343-350.

6320 Inorganic Chemistry, Vol. 41, No. 24, 2002

Copper Chemistry of â-Diketiminate Ligands

[Ph(H₂L^iPr2)Cu(MeCN)]. Crystals suitable for X-ray crystal-

lographic analysis were grown from pentane at -20 °C. The carbon

atoms of one isopropyl group were found to be disordered over

two positions, with a 63:37 occupancy ratio.

[{NO₂(H₂L^Me2Me)Cu}₂(µ-OH)₂]. Crystals suitable for X-ray

crystallographic analysis were grown from pentane diffusion into

CH₂Cl₂at -20 °C. The hydroxyl hydrogen atoms were located in

difference maps, and their positions were refined.

[3,5-(CF₃)₂C₆H₃(H₂L^iPr2)Cu(MeCN)]. Crystals suitable fo

r X-ray crystallographic analysis were grown from pentane at -20

°C. The carbon atoms of one isopropyl group were found to be

disordered over two positions, each with a 75:25 occupancy ratio.

The fluorine atoms of one of the CF₃groups were found to be

disordered over four positions. The C-F and F-F distances were

restrained to be equal. The MeCN was found to be disordered over

two positions, with an 84:16 occupancy ratio.

[Cl(Me₂L^Me2)Cu(CNC₆H₃Me₂)]. Crystals suitable for X-ray

crystallographic analysis were grown from pentane at -20 °C

overnight. The last 21 frames of data collection were omitted due

to the presence of a much higher background than all other frames

(presumably due to water condensation on the collimator).

[Cl(Me₂L^Me2)CuCl]₂. Crystals suitable for X-ray crystallographic

analysis were grown by vapor diffusion of pentane into a CH₂Cl₂

solution of the complex at -20 °C.

Acknowledgment. We thank Professor Lawrence Que,

Jr., and Dr. Raymond Ho for assistance with resonance

Raman spectroscopy, Professor John Lipscomb for access

to his EPR spectrometer, Lynneice Bowen for initial synthetic

contributions, and Nermeen Aboelella for assistance with

X-ray crystallography. Funding for this research was pro-

vided by the National Institutes of Health (Grant GM47365

to W.B.T.), the National Science Foundation (predoctoral

fellowship to A.M.R.), and the Japanese Ministry of Educa-

tion, Science, Culture, and Sports (Grants 11228206 and

13480189 to S.I.).

Supporting Information Available: Plots of magnetic suscep-

tibility data as a function of temperature for [Cl(Me₂L^Me2)CuCl]₂

at varying applied magnetic fields (Figure S1), UV-vis spectra of

[Ph(H₂L^iPr2)CuCl]₂at different temperatures (Figure S2), cyclic

voltammograms of [Ph(H₂L^iPr2)Cu(MeCN)] (Figure S3), resonance

Raman spectra of solutions of the intermediates resulting from the

reactions of Cu(I) complexes with ¹⁶O₂and ¹⁸O₂(Figure S4), and

complete X-ray crystallographic data as CIFs. This material is

available free of charge via the Internet at http://pubs.acs.org.

[H(Me₂L^Et2)CuCl]₂. Crystals suitable for X-ray crystallographic

analysis were grown from a mixture of CH₂Cl₂and HMDSO at

-20 °C. Data were collected at room temperature, since cooling

significantly below ambient temperature induced splitting of the

crystals. The chloride bridges are disordered over two sets of

positions in an 85:15 ratio. One of the ethyl groups is also

disordered, with the terminal methyl group occupying two positions

in a 65:35 ratio.

IC020369K

Inorganic Chemistry, Vol. 41, No. 24, 2002 6321

Article Doi

Copper chemistry of β-diketiminate ligands: Monomer/dimer equilibria and a new class of bis(μ-oxo)dicopper compounds

DOI: 10.1021/ic020369k

Source and publish data:

Authors:

Article abstract of DOI:10.1021/ic020369k

Full text of DOI:10.1021/ic020369k

Products guided by the article

R&D Labs maybe for 482322-43-0

Relevant to this article

Hot Product