Solution behavior and structural properties of Cu(I) complexes featuring m-terphenyl isocyanides

Article abstract of DOI:10.1021/ic8010986

The synthesis of the m-terphenyl isocyanide ligand CNAr^Mes2 (Mes = 2,4,6-Me₃C₆H₂) is described. Isocyanide CNAr^Mes2 readily functions as a sterically encumbering supporting unit for several Cu(I) halide and pseudo halide fragments, fostering in some cases rare structural motifs. Combination of equimolar quantities of CNAr ^Mes2 and CuX (X = Cl, Br and I) in tetrahydrofuran (THF) solution results in the formation of the bridging halide complexes (μ-X) ₂[Cu(THF)(CNAr^Mes2)]₂. Addition of CNAr ^Mes2 to cuprous chloride in a 2:1 molar ratio generates the complex ClCu(CNAr^Mes2)₂. in a straightforward manner. Single-crystal X-ray diffraction has revealed ClCu(CNAr^Mes2) ₂ to exist as a three-coordinate monomer in the solid state. As determined by solution ¹H NMR and FTIR spectroscopic studies, monomer ClCu(CNAr^Mes2)₂ resists tight binding of a third CNAr^Mes2 unit, resulting in rapid isocyanide exchange. Contrastingly, addition of 3 equiv of CNAr^Mes2 to cuprous iodide readily affords the tris-isocyanide species, ICu(CNAr^Mes2)₃, as determined by X-ray diffraction. Similar coordination behavior is observed in the tris-isocyanide salt [(THF)Cu(CNAr^Mes2)₃]OTf (OTf = O ₃SCF₃), which is generated upon treatment of (C ₆H₆)[Cu(OTf)]₂ with 6 equiv of CNAr ^Mes2 in THF. The disparate coordination behavior of the [CuCl] fragment relative to both [Cul] and [CuOTf] is rationalized in terms of structure and Lewis acidity of the Cu-containing fragments. The putative triflate species [Cu(CNAr^Mes2)₃]OTf itself serves as a good Lewis acid and is found to weakly bind C₆H₆ in an η¹-C manner in the solid-state. Density Functional Theory is used to describe the bonding and energetics of the η¹-C Cu-C ₆H₆ interaction.

Full text of DOI:10.1021/ic8010986

Inorg. Chem. 2008, 47, 9010-9020
Solution Behavior and Structural Properties of Cu(I) Complexes
Featuring m-Terphenyl Isocyanides
Brian J. Fox, Queena Y. Sun, Antonio G. DiPasquale, Alexander R. Fox, Arnold L. Rheingold,
and Joshua S. Figueroa*
Department of Chemistry and Biochemistry, UniVersity of California, San Diego, 9500 Gilman
DriVe, Mail Code 0358, La Jolla, California 92093-0358
Received June 14, 2008
The synthesis of the m-terphenyl isocyanide ligand CNArMes2 (Mes ) 2,4,6-Me3C6H2) is described. Isocyanide
CNArMes2 readily functions as a sterically encumbering supporting unit for several Cu(I) halide and pseudo halide
fragments, fostering in some cases rare structural motifs. Combination of equimolar quantities of CNArMes2 and
CuX (X ) Cl, Br and I) in tetrahydrofuran (THF) solution results in the formation of the bridging halide complexes
(µ-X)2[Cu(THF)(CNArMes2)]2. Addition of CNArMes2 to cuprous chloride in a 2:1 molar ratio generates the complex
ClCu(CNArMes2)2 in a straightforward manner. Single-crystal X-ray diffraction has revealed ClCu(CNArMes2)2 to exist
1
as a three-coordinate monomer in the solid state. As determined by solution H NMR and FTIR spectroscopic
studies, monomer ClCu(CNArMes2)2 resists tight binding of a third CNArMes2 unit, resulting in rapid isocyanide exchange.
Contrastingly, addition of 3 equiv of CNArMes2 to cuprous iodide readily affords the tris-isocyanide species,
ICu(CNArMes2)3, as determined by X-ray diffraction. Similar coordination behavior is observed in the tris-isocyanide
salt [(THF)Cu(CNArMes2)3]OTf (OTf ) O3SCF3), which is generated upon treatment of (C6H6)[Cu(OTf)]2 with 6 equiv
of CNArMes2 in THF. The disparate coordination behavior of the [CuCl] fragment relative to both [CuI] and [CuOTf]
is rationalized in terms of structure and Lewis acidity of the Cu-containing fragments. The putative triflate species
1
[Cu(CNArMes2)3]OTf itself serves as a good Lewis acid and is found to weakly bind C6H6 in an η -C manner in the
1
solid-state. Density Functional Theory is used to describe the bonding and energetics of the η -C Cu-C6H6
interaction.
Introduction
carbonyl metalates7 (e.g., [V(CO)6]-, [Fe(CO)4]2- and [Co-
(CO)4]-) have been prepared and studied. Although the steric
properties of isocyanides can be readily tuned, it is interesting
to note that the vast majority of reported homoleptic
isocyanide complexes feature coordination numbers identical
to, or higher than, their carbonyl analogues. This observation
As a result of their capacity to function as good σ-donors
and moderate π-acids, isocyanides (Ct N-R) have enjoyed
widespread use in transition metal chemistry as both sup-
porting ligands and reactive entities.1-3 In coordination
chemistry, isocyanides are often utilized as organic surrogates
of carbon monoxide (CO) since they provide a largely similar
ligand field4 but impart differing solubility and steric
attributes on the resultant complex. Accordingly, homoleptic
isocyanide analogues5 of the well-known transition metal
carbonyls6 (e.g., Mo(CO)6, Fe(CO)5 and Ni(CO)4) and
(6) Mo(CNR)6: R ) Ph; Mann, K. R.; Cimolino, M.; Geoffroy, G. L.;
Hammond, G. S.; Orio, A. A.; Albertin, G.; Gray, H. B. Inorg. Chim.
Acta 1976, 16, 97–101; R ) t-Bu. (a) Chiu, K. W.; Jones, R. A.;
Wilkinson, G.; Galas, A. M. R.; Hursthouse, M. B. J. Chem. Soc.,
Dalton Trans. 1981, 2088–2097. (b) Carnahan, E. M.; Lippard, S. J.
J. Chem. Soc., Dalton Trans. 1991, 699–706. R ) 2,6-Me2C6H3 (Xyl);
Yamamoto, Y.; Yamazaki, H. J. Organomet. Chem. 1985, 282, 191–
200. Fe(CNt-Bu)5: Bassett, J.-M.; Berry, D. E.; Barker, G. K.; Green,
M.; Howard, J. A. K.; Stone, F. G. A. J. Chem. Soc., Dalton Trans.
1979, 1003–1011. Ni(CNt-Bu)4: Otsuka, S.; Nakamura, A.; Tatsuno,
Y. J. Am. Chem. Soc. 1969, 91, 6994–6999.
* To whom correspondence should be addressed. E-mail: jsfig@ucsd.edu.
(1) Malatesta, L.; Bonati, F. Isocyanide Complexes of Transition Metals;
Wiley: New York, 1969.
(2) Yamamoto, Y. Coord. Chem. ReV. 1980, 32, 193–233.
(3) Bonati, F.; Minghetti, G. Inorg. Chim. Acta 1974, 9, 95–112.
(4) Sarapu, A. C.; Fenske, R. F. Inorg. Chem. 1974, 14, 247–253.
(5) Weber, L. Angew. Chem., Int. Ed. 1998, 37, 1515–1517.
(7) [V(CNXyl)6]- (Xyl ) 2,6-Me2C6H3): Barybin, M. V.; Young, V. G.,
Jr.; Ellis, J. E. J. Am. Chem. Soc. 1998, 120, 429–430. (a) [Fe(C-
NXyl)4]2-: Brennessel, W. W.; Ellis, J. E. Angew. Chem., Int. Ed.
2007, 46, 598–600. (b) [Co(CNXyl)4]-: Warnock, G. F.; Cooper, N. J.
Organometallics 1989, 8, 1826–1827.
9010 Inorganic Chemistry, Vol. 47, No. 19, 2008
10.1021/ic8010986 CCC: $40.75  2008 American Chemical Society
Published on Web 08/30/2008

Cu(I) Complexes Featuring m-Terphenyl Isocyanides
Chart 1. Some m-Terphenyl-Based Supporting Ligands
ligands, the neutral isocyano modification has received
considerably less attention as a ligating species. Indeed, in
only two reports have m-terphenyl isocyanides been em-
ployed as ligands for transition metals. Nagashima and co-
workers21 have reported the use of m-terphenyl isocyanides
in conjunction with divalent nickel halides for the polym-
erization of ethylene, while Ito and Sawamura22 have
explored their use for the Rh-catalyzed hydrosilylation of
ketones.
Notably, despite these accounts, the structural chemistry
of complexes featuring such encumbering isocyanides has
not been described. This information is particularly desirable
given that the m-terphenyl framework may be reasonably
expected to obviate the formation of high-coordinate com-
plexes. Accordingly, in this paper we present the synthesis
of the m-terphenyl isocyanide derivative CNArMes2 (Mes )
2,4,6-Me3C6H2) and detail the solution and structural be-
havior of several copper(I) halide complexes derived from
it. The selection of Cu(I) centers as a suitable coordination
platform stems from the fact that complexes of the type
XCu(CNR)n (X ) halide or pseudohalide) are a well-known
class of ionic and molecular species,23,24 which have found
Scheme 1
is adequately illustrated by the complexes Mo(CNt-Bu)66 and
K[Co(CNXyl)4] (Xyl ) 2,6-Me2C6H3),7 in which the metal
coordination number is the same as that found in the carbonyl
analogue despite the presence of several relatively encumber-
ing tert-butyl or m-xylyl substituents. Correspondingly, the
(12) For example, see:(a) Wang, Y.; Robinson, G. H. Organometallics 2007,
26, 2–11. (b) Wang, Y.; Quillian, B.; Wannere, C. S.; Wei, P.;
Schleyer, P. v. R.; Robinson, G. H. Organometallics 2007, 26, 3054–
3056. (c) Yang, X.-J.; Wang, Y.; Quillian, B.; Wei, P.; Chen, Z.;
Schleyer, P. v. R.; Robinson, G. H. Organometallics 2006, 25, 925–
929. (d) Wang, Y.; Quillian, B.; Yang, X.-J.; Wei, P.; Chen, Z.;
Wannere, C. S.; Schleyer, P. v. R.; Robinson, G. H. J. Am. Chem.
Soc. 2005, 127, 7672–7673. (e) Robinson, G. H. Chem. Commun.
2000, 2175–2181. (f) Robinson, G. H. Acc. Chem. Res. 1999, 32, 773–
782. (g) Su, J.; Li, X.-W.; Crittendon, R. C.; Campana, C. F.; Robinson,
G. H. Organometallics 1997, 16, 4511–4513.
(13) For some representative recent applications, see:(a) Filippou, A. C.;
Weidemann, N.; Philippopoulos, A. I.; Schnakenburg, G. Angew.
Chem., Int. Ed. 2006, 45, 5987–5991. (b) Filippou, A. C.; Weidemann,
N.; Schnakenburg, G.; Rohde, H.; Philippopoulos, A. I. Angew. Chem.,
Int. Ed. 2004, 43, 6512–6516. (c) Smith, R. C.; Gantzel, P.; Rheingold,
A. L.; Protasiewicz, J. D. Organometallics 2004, 23, 5124–5126. (d)
Filippou, A. C.; Philippopoulos, A. I.; Schnakenburg, G. Organome-
tallics 2003, 22, 3339–3341. (e) Smith, R. C.; Shah, S.; Urnezius, E.;
Protasiewicz, J. D. J. Am. Chem. Soc. 2003, 125, 40–41. (f) Waterman,
R.; Hillhouse, G. L. Organometallics 2003, 22, 5182–5184. (g)
Melenkivitz, R.;(h) Mindiola, D. J.; Hillhouse, G. L. J. Am. Chem.
Soc. 2002, 124, 3846–3847. (i) Shah, S.; Simpson, M. C.; Smith, R. C.;
Protasiewicz, J. D. J. Am. Chem. Soc. 2001, 123, 6925–6926. (j) Smith,
R. C.; Ren, T.; Protasiewicz, J. D. Eur. J. Inorg. Chem. 2002, 2779–
2783.
complexes [Mo(CNt-Bu)7][PF6]2 and [Ta(CNXyl)7][BF4]9
8
represent examples in which isocyanide complexes exhibit
coordination numbers greater than those found in typical
metal carbonyl species.
With the aim of generating low-coordinate, coordinatively
unsaturated isocyanide metal complexes, we have elected
to explore the coordination chemistry of isocyanide ligands
featuring the sterically encumbering m-terphenyl group
(Chart 1).10 This choice is inspired in part by the use of
m-terphenyl groups by Power,11 Robinson,12 and others13
for the stabilization of low-coordinate main group and
transition metal species of unique bonding and composition.
Whereas substituted m-terphenyl monoanions11,12 and their
amido,14-17 imido,16,18 and carboxylate19,20 derivatives have
gained prominence as sterically encumbering ancillary
(8) Carnahan, E. M.; Protasiewicz, J. D.; Lippard, S. J. Acc. Chem. Res.
1993, 26, 90–97; and references therein.
(9) Barybin, M. V.; Brennessel, W. W.; Kucera, B. E.; Minyaev, M. E.;
Sussman, V. J.; Young, V. G., Jr.; Ellis, J. E. J. Am. Chem. Soc. 2007,
129, 1141–1150.
(10) (a) Clyburne, J. A. C.; McMullen, N. Coord. Chem. ReV. 2000, 210,
73–99. (b) Twamley, B.; Haubrich, S. T.; Power, P. P. AdV.
Organomet. Chem. 1999, 44, 1–65.
(14) Gavenonis, J.; Tilley, T. D. Organometallics 2002, 21, 5549–5563.
(15) Wright, R. J.; Steiner, J.; Beaini, S.; Power, P. P. Inorg. Chim. Acta
2006, 359, 1939–1946.
(16) Gavenonis, J.; Tilley, T. D. J. Am. Chem. Soc. 2002, 124, 8536–8537.
(17) Li, J.; Song, H.; Cui, C.; Cheng, J.-P. Inorg. Chem. 2008, 47, 3468–
3470.
(11) For example, see:(a) La Macchia, G.; Gagliardi, L.; Power, P. P.;
Brynda, M. J. Am. Chem. Soc. 2008, 130, 5104–5114. (b) Rivard, E.;
Power, P. P. Inorg. Chem. 2007, 46, 10047–10064. (c) Power, P. P.
Organometallics 2007, 26, 4362–4372. (d) Wolf, R.; Brynda, M.; Ni,
C.; Long, G. J.; Power, P. P. J. Am. Chem. Soc. 2007, 129, 6076–
6077. (e) Nguyen, T.; Sutton, A. D.; Brynda, M.; Fettinger, J. C.;
Long, G. J.; Power, P. P. Science 2005, 310, 844–847. (f) Power,
P. P. Chem. Commun. 2003, 2091–2101. (g) Phillips, A. D.; Wright,
R. J.; Olmstead, M. M.; Power, P. P. J. Am. Chem. Soc. 2002, 124,
5930–5931. (h) Stender, M.; Phillips, A. D.; Wright, R. J.; Power,
P. P. Angew. Chem., Int. Ed. 2002, 41, 1785–1787. (i) Eichler, B. E.;
Power, P. P. Angew. Chem., Int. Ed. 2001, 40, 796–797. (j) Olmstead,
M. M.; Simons, R. S.; Power, P. P. J. Am. Chem. Soc. 1997, 119,
11705–11706.
(18) Gavenonis, J.; Tilley, T. D. Organometallics 2004, 23, 31–43.
(19) (a) Yoon, S.; Lippard, S. J. J. Am. Chem. Soc. 2005, 127, 8386–8397.
(b) Carson, E. C.; Lippard, S. J. J. Am. Chem. Soc. 2004, 126, 3412–
3413. (c) Carson, E. C.; Lippard, S. J. Inorg. Chem. 2006, 45, 828–
836. (d) Carson, E. C.; Lippard, S. J. Inorg. Chem. 2006, 45, 837–
848.
(20) (a) Klein, D. P.; Young, V. G., Jr.; Tolman, W. B.; Que, L., Jr. Inorg.
Chem. 2006, 45, 8006–8008. (b) Hagadorn, J. R.; Que, L., Jr.; Tolman,
W. B. Inorg. Chem. 2000, 39, 6086–6090. (c) Hagadorn, J. R.; Que,
L., Jr.; Tolman, W. B.; Prisecaru, I.; Munck, E. J. Am. Chem. Soc.
1999, 121, 9760–9761.
(21) Tanabiki, M.; Tsuchiya, K.; Kumanomido, Y.; Matsubara, K.; Mo-
toyama, Y.; Nagashima, H. Organometallics 2004, 23, 3976–3981.
(22) Ito, H.; Kato, T.; Sawamura, M. Chem. Lett. 2006, 35, 1038–1039.
Inorganic Chemistry, Vol. 47, No. 19, 2008 9011

Fox et al.
Figure 1. Molecular structure of CNArMes2. Selected bond distances (Å)
and angles (deg). C1-N1 ) 1.158(3); N1-C2 ) 1.414(3); C1-N1-C2
) 178.1(3).
Scheme 2
Figure 2. Molecular structure of (µ-Cl)2[Cu(THF)(CNArMes2)]2.
X-ray diffraction (Figure 1). In addition, solution (C6D6) and
solid state (KBr) FTIR spectra of CNArMes2 display intense
bands at 2118 cm-1 and 2120 cm-1, respectively, consistent
with the presence of a terminal isocyano unit.
Isocyanide CNArMes2 readily functions as a versatile ligand
in conjunction with copper halide salts. Addition of CNArMes2
to an equimolar amount of copper(I) chloride in tetrahydro-
furan (THF) solution generates the bridging dichloride dimer,
(µ-Cl)2[Cu(THF)(CNArMes2)]2, as determined by X-ray dif-
fraction (Scheme 2, Figure 2, Table 1). Both the bromide
and iodide congeners can be prepared in similar fashion, with
crystallographic analysis of the bromide derivative (Figure
3) revealing that it is both isomorphous and isostructural to
(µ-Cl)2[Cu(THF)(CNArMes2)]2. The solid-state FTIR spectra
of complexes (µ-X)2[Cu(THF)(CNArMes2)]2 display isocyano
stretches of 2143 cm-1, 2139 cm-1, and 2146 cm-1 for the
chloride, bromide, and iodide derivatives, respectively,
showing a modest shift to higher energy relative to that of
free CNArMes2. This later observation is consistent with the
spectroscopic behavior of other organoisocyanides upon
coordination to monovalent group 11 metals28 and is
interpreted to arise from stabilization of the filled isocyano
σ* orbital in the absence of significant π back-dona-
tion.4,28-31 Accordingly, the crystallographically determined
Ct N bond distances in complexes (µ-X)2[Cu(THF)-
(CNArMes2)]2 are not elongated relative to free CNArMes2
within experimental error and the respective Ct N-Cipso
angles do not significantly deviate from linearity (Table 1).
An interesting structural characteristic of complexes (µ-
X)2[Cu(THF)(CNArMes2)]2, however, is the noticeably obtuse
C(1)-Cu(1)-Cu(1a) angles relating the anti-disposed
CNArMes2 ligands (155.37(6)° and 153.85(10)° for the Cl and
Br derivatives, respectively). This relatively large spacing
between isocyanide ligands in complexes (µ-X)2[Cu(THF)-
(CNArMes2)]2 is proposed to manifest from the weak σ-donat-
ing capacity of THF, rather than from steric pressures
associated with ArMes2 units. Lending credence to this notion
is the finding that pyridine (py) readily displaces the
utility as reagents for organic transformations,25 supramo-
lecular templating agents,26 and enzymatic probes.27 As
delineated herein, the encumbering nature of the m-terphenyl
framework reliably controls the extent of isocyanide ligation
and fosters rare structural motifs within the context of Cu(I)
isocyanide chemistry.
Results and Discussion
The synthesis of m-terphenyl isocyanide CNArMes2 is
depicted in Scheme 1. Treatment of the amine H2NArMes2
with excess formic acid readily provides the corresponding
formaniline, HC(O)N(H)ArMes2, in excellent yield. Dehydra-
tion of HC(O)N(H)ArMes2 with OPCl3 in the presence of base
generates the isocyanide CNArMes2 as a colorless solid after
work up. Isocyanide CNArMes2 has been fully characterized
by 1H and 13C NMR, combustion analysis, and single crystal
(23) For representative early accounts, see: (a) Irving, H.; Jonason, M.
J. Chem. Soc. 1960, 2095–2097. (b) Fisher, P. J.; Taylor, N. E.;
Harding, M. M. J. Chem. Soc. 1960, 2303–2309. (c) Otsuka, S.; Mori,
K; Yamagami, K. J. Org. Chem. 1966, 31, 4170–4174. (d) Bailey, J.;
Mays, M. J. J. Organomet. Chem. 1973, 47, 217–224.
(24) Bell, A.; Walton, R. A.; Edwards, D. A.; Poulter, M. A. Inorg. Chim.
Acta 1985, 104, 171–178.
(25) For example:(a) Kamijo, S.; Kanazawa, C.; Yamamoto, Y. J. Am.
Chem. Soc. 2005, 127, 9260–9266. (b) Fiaschi, P.; Floriani, C.;
Pasquali, M.; Chiesi-Villa, A.; Guastini, C. Inorg. Chem. 1986, 25,
462–469. (c) Wakselman, C.; Tordeux, M. J. Org. Chem. 1979, 44,
4219–4220. (d) Tsuda, T.; Habu, H.; Horiguchi, S.; Saegusa, T. J. Am.
Chem. Soc. 1974, 96, 5930–5931.
(26) (a) Benouazzane, M.; Coco, S.; Espinet, P.; Barbera, J. Inorg. Chem.
2002, 41, 5754–5759. (b) Benouazzane, M.; Coco, S.; Espinet, P.;
Barbera, J. J. Mater. Chem. 2001, 11, 1740–1744.
(28) Robertson, M. J.; Angelici, R. J. Langmuir 1994, 10, 1488–1492.
(29) Shih, K.; Angelici, R. J. Langmuir 1995, 11, 2539–2546.
(30) Henderson, J. I.; Feng, S.; Bein, T.; Kubiak, C. P. Langmuir 2000,
16, 6183–6187.
(27) Reedy, B. J.; Murthy, N. N.; Karlin, K. D.; Blackburn, N. J. J. Am.
Chem. Soc. 1995, 117, 9826–9831.
(31) Hattori, R.; Suzuki, E.; Shimizu, K. J. Mol. Struct. 2005, 738, 165–
170.
9012 Inorganic Chemistry, Vol. 47, No. 19, 2008

Cu(I) Complexes Featuring m-Terphenyl Isocyanides
Table 1. Selected Bond Distances (Å) and Angles (deg) for
(µ-Cl)2[Cu(THF)(CNArMes2)]2, (µ-Br)2[Cu(THF)(CNArMes2)]2, and
(µ-Cl)2[Cu(py)(CNArMes2)]2
(µ-Cl)2[Cu(THF)(CNArMes2)]2
C1-N1
1.165(2)
1.829(2)
C1-Cu1
Cu1-Cl1
Cu1-O1
2.3525(6)
2.1912(14)
2.3101(5)
174.4(2)
173.21(19)
102.68(7)
119.26(7)
96.22(4)
132.46(6)
100.534(19)
97.32(4)
79.466(19)
155.37(6)
Cu1-Cl1A
C1-N1-C2
N1-C1-Cu1
C1-Cu1-O1
C1-Cu1-Cl1
O1-Cu1-Cl1
C1-Cu1-Cl1A
Cl1-Cu1-Cl1A
O1-Cu1-Cl1A
Cu1-Cl1-Cu1A
C1-Cu1-Cu1A
Figure 3. Molecular structure of (µ-Br)2[Cu(THF)(CNArMes2)]2.
(µ-Br)2[Cu(THF)(CNArMes2)]2
C1-N1
1.155(4)
1.849(3)
2.4657(5)
2.183(2)
C1-Cu1
Cu1-Br1
Cu1-O1
Cu1-Br1A
2.4306(5)
175.2(3)
171.9(3)
101.68(11)
116.58(10)
98.33(6)
129.91(10)
105.417(17)
97.78(6)
C1-N1-C2
N1-C1-Cu1
C1-Cu1-O1
C1-Cu1-Br1
O1-Cu1-Br1
C1-Cu1-Br1A
Br1-Cu1-Br1A
O1-Cu1-Br1A
Cu1-Br1-Cu1A
C1-Cu1-Cu1A
74.583(17)
153.85(10)
Figure 4. Molecular structure of (µ-Cl)2[Cu(py)(CNArMes2)]2.
(µ-Cl)2[Cu(py)(CNArMes2)]2
Scheme 3
C1-N1
1.151(6)
1.854(4)
2.4735(15)
2.057(4)
2.3183(14)
177.3(5)
C1-Cu1
Cu1-Cl1
Cu1-N2
Cu1-Cl1A
C1-N1-C2
N1-C1-Cu1
C1-Cu1-N2
C1-Cu1-Cl1
N2-Cu1-Cl
C1-Cu1-Cl1A
Cl1-Cu1-Cl1A
N2-Cu1-Cl1A
Cu1-Cl1-Cu1A
C1-Cu1-Cu1A
170.9(5)
115.13(18)
106.46(15)
96.94(12)
129.76(16)
99.85(4)
102.90(11)
80.15(4)
135.01(10)
coordinated THF ligands in (µ-Cl)2[Cu(THF)(CNArMes2)]2
to provide the dimeric pyridine adduct (µ-Cl2)[Cu-
(py)(CNArMes2)]2 (Scheme 2). Structural characterization of
the latter (Figure 4, Table 1) reveals that pyridine induces
significantly greater contraction of the corresponding
C(1)-Cu(1)-Cu(1a) angle (135.01(10)°) and that this
geometric distortion is readily accommodated by the
CNArMes2 ligands.
In contrast to the dimeric species described above,
monomeric Cu(I) complexes are readily obtained when two
or more CNArMes2 ligands are employed. For example,
combination of cuprous chloride and CNArMes2 in a 1:2 molar
ratio in CH2Cl2 solution allows for the isolation of the three-
coordinate, bis-isocyanide complex ClCu(CNArMes2)2 (Scheme
3). Addition of a second molar equivalent of cuprous chloride
to ClCu(CNArMes2)2 in THF generates (µ-Cl)2[Cu(THF)-
(CNArMes2)]2 as determined by 1H NMR spectroscopy, thus
indicating that CNArMes participates in ligand redistribution
reactions under suitable conditions. Like the dinuclear Cu(I)
complexes discussed above, ClCu(CNArMes2)2 gives rise to
an intense FTIR ν(CN) stretch centered at 2143 cm-1, which
is slightly higher in energy than that found for free CNArMes2
.
The molecular structure of ClCu(CNArMes2
) has been
2
determined by X-ray diffraction and is shown in Figure 5.
The most interesting structural aspects of ClCu(CNArMes2
)
2
are its trigonal planar coordination geometry and the
perpendicular disposition of the ArMes2 central aryl rings with
respect to the Cu-containing plane. As visualized from space-
filling models of ClCu(CNArMes2)2 (Figure 6), this latter
attribute results in a substantial steric shield around roughly
one-third of the Cu primary coordination sphere. However,
Inorganic Chemistry, Vol. 47, No. 19, 2008 9013

Fox et al.
Scheme 4
workers34 reported the structure of ClCu(CNt-Bu)2, which
is the first example of a structurally characterized monomeric,
XCu(CNR)2 (X ) halide) species. However, this complex
was obtained as a byproduct in very low yield during the
synthesis of the tetrakis-isocyanide salt [Cu(CNt-Bu)4]Cl, and
a straightforward synthesis has not been disclosed. We
therefore suggest that the reliable synthesis and isolation of
monomeric ClCu(CNArMes2)2 in bulk can be reasonably
attributed to the steric properties of the CNArMes ligand.
Whereas ClCu(CNArMes2)2 is amenable to isolation, a third
CNArMes2 ligand is not readily accommodated by the [CuCl]
Figure 5. Molecular structure of ClCu(CNArMes2)2. Selected bond distances
(Å) and angles (deg): C1-N1 ) 1.160(2); Cu1-C1 ) 1.8993(17); Cu1-Cl1
) 2.2445(6); C1-N1-C2 ) 176.60(15); C1-Cu1-C1A ) 120.85(10);
C1-Cu1-Cl1 ) 119.58(5); C1A-Cu1-Cl1 ) 119.58(5).
1
fragment. Room temperature H NMR spectra of CD2Cl2
solutions containing equimolar quantities of ClCu(CNArMes2
)
2
and CNArMes2 exhibit sharp resonances at chemical shifts
corresponding to the weighted average of the two species.
Analogous spectroscopic behavior is observed for 1:2 ClCu(C-
NArMes2)2/CNArMes2 mixtures in the same solvent, strongly
indicating rapid exchange of free and coordinated CNArMes2
on the 1H NMR time scale. In accord with the kinetic lability
of the d10 Cu(I) ion,35 ligand exchange in this system is facile
as demonstrated by the finding that the composite ArMes2
resonances in 1:1 ClCu(CNArMes2)2/CNArMes2 mixtures first
1
begin to broaden at -40 °C when assayed by H NMR
spectroscopy (CD2Cl2). Isocyanide exchange is further cor-
roborated by FTIR spectroscopy. Room temperature C6D6
solutions containing equal quantities of ClCu(CNArMes2)2 and
CNArMes2 exclusively exhibit distinct νCN stretches attribut-
able to both species, with no spectroscopic evidence for the
formation of a new complex. However, it is important to
note that free CNArMes2 is not observed in the FTIR spectrum
of pure ClCu(CNArMes2)2 in C6D6 solution. This latter detail
suggests that ClCu(CNArMes2)2 retains its integrity in solution
and does not readily undergo ligand redistribution or
Figure 6. Space filling diagrams of ClCu(CNArMes2)2. Top: View
orthogonal to the trigonal plane. Bottom: View of the steric shield provided
by the two ArMes2 units. Orange ) Cu, Green ) Cl.
exchange reactions in the absence of an additional cuprous
32
chloride or CNArMes2. As pointed out by Floriani,
the
despite the seemingly close-packed nature of the isocyanide
ligands in ClCu(CNArMes2)2, hindered rotation of the ArMes2
residues is not observed on the 1H NMR time scale at 20 °C
in C6D6 or at -60 °C in CD2Cl2 solution.
inherent lability of the Cu(I)-isocyanide linkage leads to
complex [Cu(CNR)n]x speciation patterns in solution. For this
Cu(I)/CNArMes2 system, however, well-defined complexes are
available in solution when agents which may induce ligand
redistribution or exchange are not present.
Unlike cuprous chloride, addition of 3 equiv of CNArMes2
to cuprous iodide affords the isolable tris-isocyanide complex
ICu(CNArMes2)3 under straightforward synthetic conditions
(Scheme 4). In solution at 20 °C, ICu(CNArMes2)3 gives rise
Interestingly, ClCu(CNArMes2
) represents a very rare
2
example of a structurally authenticated monomeric bis-
isocyanide Cu(I) halide complex. Indeed, most related Cu
bis-isocyanide examples contain the (µ-halide)2 functionality
in the solid state.32,33 Only recently have Bowmaker and co-
(32) Toth, A.; Floriani, C.; Chiesi-Villa, A.; Gaustini, C. J. Chem. Soc.,
Dalton Trans. 1988, 1599–1605.
(33) Reference 25a reports several examples of (µ-X)2[Cu(CNR)2]2 com-
plexes (X ) Cl, Br, I) proposed on the basis of powder X-ray
diffraction experiments.
(34) Bowmaker, G. A.; Hanna, J. V.; Hahn, F. E.; Lipton, A. S.; Oldham,
C. E.; Skelton, B. W.; Smith, M. E.; White, A. H. Dalton Trans. 2008,
1710–1720.
(35) (a) Frei, U. M.; Geier, G. Inorg. Chem. 1992, 31, 187–190. (b) Frei,
U. M.; Geier, G. Inorg. Chem. 1992, 31, 3132–3137.
9014 Inorganic Chemistry, Vol. 47, No. 19, 2008

Cu(I) Complexes Featuring m-Terphenyl Isocyanides
Figure 8. Molecular structure of [(THF)Cu(CNArMes2)3]OTf. Selected bond
distances (Å) and angles (deg): Cu1-C1 ) 1.931(3); Cu1-C2 ) 1.921(3);
Cu1-C3 ) 1.916(3); Cu1-O1 ) 2.182(2); C1-N1 ) 1.148(4); C2-N2
) 1.159(4); C3-N3 ) 1.154(4); C1-Cu1-C2 ) 117.50(13); C1-Cu1-C3
) 119.04(13); C2-Cu1-C3 ) 119.14(13); O1-Cu1-C1 ) 96.06(11);
O1-Cu1-C2 ) 95.54(11); O1-Cu1-C3 ) 99.21(11).
Figure 7. Molecular structure of ICu(CNArMes2)3. Selected bond distances
(Å) and angles (deg) for ICu(CNArMes2)3. Cu1-C1 ) 1.941(3); Cu1-C2
) 1.933(3); Cu1-C3 ) 1.942(3); C1-N1 ) 1.164(3); C2-N2 ) 1.154(3);
C3-N3 ) 1.160(3); C1-Cu1-C2 ) 115.51(11); C1-Cu1-C3 )
117.18(10); C2-Cu1-C3 ) 115.93(10); C1-Cu1-I1 ) 101.73(7);
C2-Cu1-I1 ) 102.40(8); C3-Cu1-I1 ) 100.02(8).
reflects a snapshot along the continuum of dissociation of
the I-Cu(I) unit consistent with the ability of iodide to serve
as a good leaving group.
Scheme 5
To this end, utilization of triflate ([F3CSO3]-, OTf) in place
of iodide leads to a tris-isocyanide complex in which the
anion is fully dissociated. Thus, treatment of (C6H6)[Cu-
(OTf)]2 with 6.0 equiv of CNArMes2 in THF (Scheme 5)
readily provides the tris-isocyanide THF adduct,
[(THF)Cu(CNArMes2)3]OTf, as a well-separated cation/anion
pair (Figure 8). Calculation of the τ4 parameter for
[(THF)Cu(CNArMes2)3]OTf results in a value of 0.86, which
is clearly indicative of a trigonal pyramidal four-coordinate
geometry and reflects the inability of THF to significantly
pyramidalize the [Cu(CNR)3]+ core. Furthermore, simple
addition of CNArMes2 to (C6H6)[CuOTf]2 does not generate
a tetrakis-isocyanide Cu(I) derivative despite the weakly
coordinating nature of the triflate anion. This observation
signifies that the CNArMes2 ligand can foster low-coordinate
species under suitable conditions since complexes of the type
[Cu(CNR)4]X are commonly encountered with less encum-
bering isocyanides.32,34,37,38
The fact that both cuprous iodide and cuprous triflate
afford tris-CNArMes2 complexes, while cuprous chloride does
not, is particularly curious. To ascertain whether a tris-
isocyanide chloride complex is inherently destabilized in
conjunction with CNArMes2, the triflate species [(THF)Cu-
(CNArMes2)3]OTf was treated with external chloride sources.
As depicted in Scheme 5, treatment of [(THF)Cu-
(CNArMes2)3]OTf with either LiCl or [NBu4]Cl in THF
solution generates ClCu(CNArMes2)2 concomitant with the
release of a CNArMes2 ligand.39 Therefore, we propose that
to a single set of ArMes2 resonances in its 1H NMR spectrum
which remains sharp down to -60 °C (CD2Cl2). Thus,
CNArMes2 dissociation does not appear to be taking place at
ambient or cooler temperatures. As depicted in Figure 7,
ICu(CNArMes2)3 exists as a pseudo C3-symmetric monomer
in the solid state by virtue of the propeller-like arrangement
of its three ArMes2 residues. The important Cu-based metric
parameters for ICu(CNArMes2)3 match well with the iodo tris-
isocyanide complex, ICu(CN(p-Tol))3,32 signifying that the
encumbering ArMes2 groups do not impart a ligand-enforced
geometry on the Cu center. Accordingly, the Cu coordination
geometry in ICu(CNArMes2)3 is best described as intermediate
between tetrahedral and trigonal pyramidal extremes. Cal-
culation of Houser’s τ4 four-coordinate geometry index36
supports this claim and results in a value of 0.90 for
ICu(CNArMes2)3, which is conservatively midrange between
idealized tetrahedral (τ4 ) 1.0) and trigonal pyramidal (τ4
) 0.85). While subtle, we speculate that this distortion
(37) Knol, D.; Koole, N. J.; de Bie, M. J. A. Org. Magn. Reson. 1976, 8,
213–218.
(38) Kitagawa, S.; Munakata, M. Inorg. Chem. 1984, 23, 4388–4390.
(39) Data in support of CNArMes2 ejection from copper upon chloride
ligation include 1H NMR and FTIR spectra (solution and solid-state)
that are identical to those produced in the isocyanide exchange studies
outlined above. In addition, an 19F{1H} NMR signal is not observed
from the C6D6 soluble fraction after [(THF)Cu(CNArMes2)3]OTf is
treated with LiCl.
(36) Yang, L.; Powell, D. R.; Houser, R. P. Dalton Trans. 2007, 955–964.
Inorganic Chemistry, Vol. 47, No. 19, 2008 9015

Fox et al.
down the pseudo 3-fold axis reveals that only one carbon
atom is situated directly over the Cu center (Figure 9,
bottom). Whereas several η2-arene complexes of Cu(I) are
known,44-50 η1-C coordination has not previously been
established for a Cu center and is rare in general.51-58
Furthermore, of the η1-C arene-metal interactions structurally
verified, only two examples51,53 exist in which the arene unit
is unsupported by a larger ligand framework. Although the
Cu-C4 bond length of 2.715
Å
in [(η1-C-C6H6)-
Cu(CNArMes2)3]OTf is long when compared to other structur-
ally characterized η1-C arene complexes, aspects of its
structure point to the existence of a weak interaction between
C6H6 and the central Cu atom. These include (i) the angular
canting of C4 and H4A in the direction of the Cu center and
(ii) the concomitant slight pyramidalization of the Cu
center in the direction opposite of the C6H6 molecule
(Σ(∠Ciso-Cu-Ciso) ) 355.14°). In addition, one ArMes2
residue is observed to rotate orthogonally to the other two,
seemingly adjusting to accommodate the presence of the
C6H6 molecule. Taken together, these structural attributes
reflect an electronic and steric perturbation of the [Cu(C-
NArMes2)3]+ core which would not be expected simply from
a C6H6 molecule of co-crystallization.
To further probe the close Cu-C6H6 contact in [(η1-C-
C6H6)Cu(CNArMes2)3]OTf, the computational model [(η1-C-
C6H6)Cu(CNArPh2)3]+ was studied using density functional
theory (DFT). As shown in Figure 10, the optimized structure
of [(η1-C-C6H6)Cu(CNArPh2)3]+ matches well with its ex-
perimental counterpart and does not converge to an η2-C6H6
minimum. Furthermore, the C6H6 unit remains angled and
within close proximity to the Cu center. Analysis of the
electronic structure of [(η1-C-C6H6)Cu(CNArPh2)3]+ does
reveal a low-lying filled molecular orbital (HOMO-22)
indicative of bonding between Cu and the proximal carbon
atom of the C6H6 molecule (Figure 11). Also apparent is
that a binodal, e1g-type orbital is used by C6H6 to bind to
the Cu center. Most interestingly, the p-orbital coefficients
Figure 9. Molecular structure of [(η1-C-C6H6)Cu(CNArMes2)3]OTf. Top:
perspective view. Bottom: View down the pseudo 3-fold axis of the
[Cu(CNArMes2)3] fragment. Hydrogen atoms of the [Cu(CNArMes2)3] frag-
ment have been omitted for clarity. Selected bond distances (Å) and angles
(deg). Cu1-C4 ) 2.715(5); Cu1-H4A ) 2.659(5); Cu1-C5 ) 3.194(5);
Cu1-C9 ) 3.165(5); Cu1-C1 ) 1.921(5); Cu1-C2 ) 1.923(5); Cu1-C3
) 1.939(4); d(Ct N)av ) 1.159 ( 0.009; C4-C5 ) 1.378(7); C4-C9 )
1.369(7); d(C-C, C6H6)av ) 1.373 ( 0.009; C1-Cu1-C2 ) 122.00(19);
C1-Cu1-C3 ) 121.69(18); C2-Cu1-C3 ) 111.44(18).
tight binding of a third CNArMes2 ligand to ClCu(CNArMes2
)
2
(44) Turner, R. W.; Amma, E. L. J. Am. Chem. Soc. 1963, 85, 4046–4047.
(45) Dines, M. B.; Bird, P. H. J. Chem. Soc., Chem. Commun. 1973, 1,
12–12.
(46) Rodesiler, P. F.; Amma, E. L. J. Chem. Soc. Chem. Commun. 1974,
599–600.
(47) Dattelbaum, A. M.; Martin, J. D. Inorg. Chem. 1999, 38, 6200–6205.
(48) Laitar, D. S.; Mathison, C. J. N.; Davis, W. M.; Sadighi, J. P. Inorg.
Chem. 2003, 42, 7354–7356.
(49) Hamilton, C. W.; Laitar, D. S.; Sadighi, J. P. Chem. Commun. 2004,
1628–1629.
(50) Amisial, L. D.; Dai, X.; Kinney, R. A.; Krishnaswamy, A.; Warren,
T. H. Inorg. Chem. 2004, 43, 6537–6539.
(51) Lau, W.; Huffman, J. C.; Kochi, J. K. J. Am. Chem. Soc. 1982, 104,
5515–5517.
(52) Chen, H.; Bartlett, R. A.; Olmstead, M. M.; Power, P. P.; Shoner,
S. C. J. Am. Chem. Soc. 1990, 112, 1048–1055.
(53) Batsanov, A. S.; Crabtree, S. P.; Howard, J. A. K.; Lehmann, C. W.;
Kilner, M. J. Organomet. Chem. 1998, 550, 59–61.
(54) Albrecht, M.; Spek, A. L.; van Koten, G. J. Am. Chem. Soc. 2001,
123, 7233–7246.
is disfavored as a result of the attenuated Lewis acidity of
the [CuCl] fragment relative to either [CuI]40 or [CuOTf],41
rather than steric inaccessibility posed by the ArMes2 residues.
Accordingly, it has been noted that [CuI] and [CuOTf] salts
can function as more efficient Lewis acid catalysts for organic
transformations than their [CuCl] analogues.41,42
With respect to the Lewis acidity of the [Cu(CNArMes2)3]+
fragment, it is notable that crystallization of putative
[[Cu(CNArMes2)3]OTf] from dilute C6H6 solution afforded a
species which, in the solid state, may reasonably be described
as possessing a weak η1-C Cu-benzene interaction.43 As
shown in Figure 9 (top), the C6H6 molecule in [(η1-C-
C6H6)Cu(CNArMes2)3]OTf docks at an angle within the
protective framework of the three CNArMes2 ligands. A view
(55) Geldbach, T. J.; Drago, D.; Pregosin, P. S. J. Organomet. Chem. 2002,
643, 214–222.
(40) Singh, P. P.; Srivatava, S. K.; Srivatava, A. K. J. Inorg. Nucl. Chem.
1980, 42, 521–532.
(41) Yamamoto, Y. J. Org. Chem. 2007, 72, 7817–7831.
(42) Ma, B.; Snyder, J. K. Organometallics 2002, 21, 4688–4695.
(43) Hubig, S. M.; Lindeman, S. V.; Kochi, J. K. Coord. Chem. ReV. 2000,
200, 831–873.
(56) Reid, S. M.; Boyle, R. C.; Mague, J. T.; Fink, M. J. J. Am. Chem.
Soc. 2003, 125, 7816–7817.
(57) Krumper, J. R.; Gerisch, M.; Magistrato, A.; Rothlisberger, U.;
Bergman, R. G.; Tilley, T. D. J. Am. Chem. Soc. 2004, 126, 12492–
12502.
(58) Barder, T. E. J. Am. Chem. Soc. 2006, 128, 898–904.
9016 Inorganic Chemistry, Vol. 47, No. 19, 2008

Cu(I) Complexes Featuring m-Terphenyl Isocyanides
In conclusion, the m-terphenyl isocyanide framework
functions as a versatile supporting group for monovalent Cu
centers. As revealed from crystallographic studies, the
compliment of either two or three ligated CNArMes2 units
provides an effective steric shield around a central metal
center. Given the portability of the isocyano moiety to large
number of transition metal fragments, it is anticipated that
derivatized m-terphenyl isocyanide ligands will engender the
formation of reactive, low coordinate species capable of
productive transformations of exogenous substrates.
Experimental Section
General Considerations. All manipulations were carried out
under an atmosphere of dinitrogen using standard Schlenk and
glovebox techniques. Solvents were dried and deoxygenated
according to standard procedures. Unless otherwise stated, reagent
grade starting materials were purchased from commercial sources
and used as received. Benzene-d6, methylene chloride-d2, and
chloroform-d (Cambridge Isotope Laboratories) were degassed and
stored over 4 Å molecular sieves for 2 d prior to use. The aniline14,15
Figure 10. DFT minimized molecular structure of model [(η1-C-
C6H6)Cu(CNArPh2)3]+. Selected bond distances (Å) and angles (deg).
Cu1-C4 ) 2.769; Cu1-H4A ) 2.713; Cu1-C5 ) 3.317; Cu1-C9 )
3.276; Cu1-C1 ) 1.881; Cu1-C2 ) 1.886; Cu1-C3 ) 1.902; d(Ct N)av
) 1.173 ( 0.005; d(C-C, C6H6)av ) 1.399 ( 0.004; C1-Cu1-C2 ) 122.3;
C1-Cu1-C3 ) 122.3; C2-Cu1-C3 ) 110.4. Numbering scheme follows
that of the X-ray structure for [(η1-C-C6H6)Cu(CNArMes2)3]OTf.
60
H2NArMes2 and (C6H6)[Cu(OTf)]2 were prepared as described
previously. LiCl and KBr were stirred overnight in anhydrous THF,
filtered, and dried under vacuum (24 h) at a temperature above
250 °C prior to use. [NBu4]Cl was subjected to three cycles of
stirring in anhydrous THF and drying in vacuo prior to use. Solution
1H, 13C{1H} and 19F NMR spectra were recorded on Varian Mercury
300 and 400 spectrometers. 1H and 13C chemical shifts are reported
in ppm relative to SiMe4 (1H and 13C δ ) 0.0 ppm) with reference
to residual solvent resonances of 7.16 ppm (1H) and 128.06 ppm
(13C) for benzene-d6, 5.32 ppm (1H) for methylene chloride-d2, and
7.26 ppm (1H) and 77.1 ppm (13C) for chloroform-d. 19F NMR
spectra were referenced externally to neat trifluoroacetic acid,
F3CC(O)OH (δ ) -78.5 ppm vs CFCl3 ) 0.0 ppm). FTIR spectra
were recorded on a Thermo-Nicolet Avatar 380 FT-IR spectrometer
as either KBr pellets or as C6D6 solutions in a ThermoFisher
solution cell equipped with KBr windows. For solution FTIR
spectra, solvent peaks were digitally subtracted from all spectra by
comparison with an authentic spectrum obtained immediately prior
to that of the sample. Combustion analyses were performed by
Robertson Microlit Laboratories, Madison, NJ.
Synthesis of HC(O)NHArMes2. To a toluene solution of
H2NArMes2 (13.45 g, 40.8 mmol, 200 mL) was added formic acid
(HCOOH, 28.18 g, 612.3 mmol, 15 equiv). The resulting yellow
mixture was refluxed in a Dean-Stark apparatus with periodic
readdition of condensed HCOOH. After 12 h, all volatile materials
were removed under reduced pressure affording HC(O)NHArMes2
colorless solid, which was washed with Et2O (3 × 20 mL) and
hexanes (2 × 30 mL) before being dried in vacuo. Yield: 10.99 g,
Figure 11. Molecular orbital 214 (HOMO-22) in [(η1-C-C6H6)-
Cu(CNArPh2)3]+ describing the primary η1-C C6H6-Cu bonding interaction.
Isosurface value ) 0.03 au.
of both “ortho” carbon atoms of this orbital vanish, reflecting
the symmetry lowering of the C6H6 unit brought about
by the η1 C-Cu interaction. However, calculation
of ∆HSCF for the hypothetical reaction C6H6 + [Cu(C-
NArPh2)3]+ f [(η1-C-C6H6)Cu(CNArPh2)3]+ results in an
enthalpic driving force of only 3.0 kcal/mol for η1-C6H6
binding.59 Thus, while manifest in the solid state, it is
doubtful that such an interaction is strongly preserved in
solution by the cationic [Cu(CNArMes2)3]+ fragment. Ac-
cordingly, as Tilley and co-workers57 have shown, η1-C
M-arene interactions can be persistent and spectroscopically
observable in solution when buttressed by the framework of
a multidentate ligand.
1
30.7 mmol, 75.3%. H NMR (300.1 MHz, CDCl3, 20 °C): δ )
7.63 (d, 1H, J ) 6 Hz, HC(O)NH), 7.32 (t, 1H, J ) 7 Hz, p-Ph),
7.14 (d, 2H, J ) 7 Hz, m-Ph), 6.96 (s, 4H, m-Mes), 6.60 (br d, 1H,
J ) 6 Hz, HC(O)NH), 2.32 (s, 6H, p-CH3), 2.01 (s, 12H, o-CH3)
ppm. 13C{1H} NMR (100.6 MHz, CDCl3, 20 °C): δ ) 162.7
(CdO), 138.0, 135.9, 134.5, 133.4, 132.3, 130.3, 129.0, 126.0, 21.2
(p-CH3), 20.4 (o-CH3) ppm. FTIR (KBr pellet) (νCO) 1682 cm-1
also 3358 (νNH), 2972, 2912, 2854, 1612, 1492, 1456, 1410, 1377,
1276, 1207, 1178, 860, 813, 764 cm-1. Anal. Calcd for C25H27NO:
C, 83.99; H, 7.61; N, 3.92. Found: C, 83.74; H, 7.71; N, 3.77.
Synthesis of CNArMes2. To a CH2Cl2 solution of HC(O)N-
HArMes2 (9.29 g, 25.99 mmol, 150 mL) was added diisopropylamine
(59) It is pertinent to note that model [Cu(CNArPh2)3]+ optimized to a
structure containing a planar Cu atom (Σ(∠Ciso-Cu-Ciso) ) 359.4°,
Supporting Information, Figure S2-1). This observation lends credence
to the notion that the presence of a C6H6 molecule perturbs the Cu
coordination geometry in [(η1-C-C6H6)Cu(CNArMes2)3]OTf.
(60) Salomon, R. G.; Kochi, J. K. J. Am. Chem. Soc. 1973, 95, 3300–
3310.
Inorganic Chemistry, Vol. 47, No. 19, 2008 9017

Fox et al.
Table 2. Crystallographic Data and Refinement Information
CNArMes
(µ-Cl)2[Cu(THF)(CNArMes2)]2 ·THF
(µ-Br)2[Cu(THF)(CNArMes2)]2 ·THF
formula
crystal system
space group
a, Å
b, Å
c, Å
C25H25N
orthorhombic
Pbca
17.304(2)
7.9368(10)
28.327(4)
90
90
90
3890.5(9)
8
C62H74Cl2Cu2N2O3
monoclinic
P21/n
8.2737(4)
11.4673(6)
29.3505(14)
90
95.7120(10)
90
2770.9(2)
2
C62H74Br2Cu2N2O3
monoclinic
P21/n
8.2999(6)
11.6485(9)
29.157(2)
90
95.2910(10)
90
2807.0(4)
2
R, deg
ꢀ, deg
γ, deg
V, Å3
Z
F (calcd), g/cm3
µ (Mo KR), mm-1
θ max, deg
data/parameters
R1
1.159
0.066
25.35
3556/242
0.0535
0.1258
1.006
1.310
0.910
28.27
6394/304
0.0398
1.399
2.227
26.37
5748/298
0.0420
wR2
GOF
0.0922
1.052
0.1025
1.018
(µ-Cl)2[Cu(py)(CNArMes2)]2 ·C6H12
ClCu(CNArMes2)2 ·4CH2Cl2
ICu(CNArMes2)3 ·8THF
C107H139CuIN3O8
formula
crystal system
space group
a, Å
b, Å
c, Å
C66H72Cl2Cu2N4
monoclinic
P21/n
C54H58Cl9CuN2
monoclinic
C2/c
triclinic
j
P1
8.386(3)
11.429(4)
29.257(10)
90
94.965(6)
90
26.8408(15)
9.1119(5)
24.5812(14)
90
115.0380(10)
90
14.5797(14)
14.8369(14)
24.492(2)
83.6590(10)
72.7190(10)
85.1320(10)
5020.4(8)
2
R, deg
ꢀ, deg
γ, deg
V, Å3
2793.7(17)
2
5446.9(5)
4
Z
F (calcd), g/cm3
µ (Mo KR), mm-1
θ max, deg
data/parameters
R1
1.331
0.902
25.03
4718/340
0.0775
0.2004
1.027
1.363
0.880
28.13
6170/305
0.0322
1.157
0.578
26.37
20297/739
0.0434
wR2
GOF
0.0764
1.048
0.1004
0.846
[(THF)Cu(CNArMes2)3]OTf·THF
[(η1-C-C6H6)Cu(CNArMes2)3]OTf
formula
crystal system
space group
a, Å
b, Å
c, Å
C84H91CuF3N3O5S
monoclinic
P21/n
12.0551(9)
34.396(3)
18.6865(14)
90
94.7720(10)
90
7721.4(10)
4
C82H81CuF3N3O3S
orthorhombic
P212121
13.649(3)
20.164(4)
25.500(5)
90
90
90
7018(2)
4
R, deg
ꢀ, deg
γ, deg
V, Å3
Z
F (calcd), g/cm3
µ (Mo KR), mm-1
θ max, deg
data/parameters
R1
1.183
0.368
25.03
13644/892
0.0569
1.239
0.400
25.56
13008/838
0.0576
0.1322
1.008
wR2
GOF
0.1056
1.022
(9.21 g, 91.0 mmol, 3.5 equiv). The solution was cooled to 0 °C
under an N2 atmosphere and POCl3 (4.38 g, 28.6 mmol, 1.1 equiv)
was added dropwise via syringe. The resulting mixture was allowed
to stir for 3 h, after which 80 mL of an aqueous 1.5 M Na2CO3
was transferred via cannula. After an additional 12 h of stirring,
the organic and aqueous layers were separated, and the latter was
washed with CH2Cl2 (3 × 50 mL). The combined CH2Cl2 extracts
were dried with MgSO4,, filtered and dried in vacuo, affording
isocyanide CNArMes2 as a colorless solid. Yield: 7.50 g, 22.1 mmol,
85.0%. 1H NMR (500.3 MHz, C6D6, 20 °C): δ ) 6.97 (t, 1H, J )
8 Hz, p-Ph), 6.85 (s, 4H, m-Mes), 6.84 (d, 2H, J ) 8 Hz, m-Ph),
2.16 (s, 6H, p-CH3), 2.05 (s, 12H, o-CH3) ppm. 13C{1H} NMR
(100.6 MHz, C6D6, 20 °C): δ ) 170.7 (Ct N), 139.9, 137.8, 135.7,
134.8, 129.4, 129.3, 128.9, 95.7, 21.2 (p-CH3), 20.3 (o-CH3) ppm.
FTIR (KBr pellet): (νCN) 2120 cm-1 also 2999, 2970, 2944, 2916,
2854, 1613, 1457, 1416, 1378, 862, 853, 807, 787, 760 cm-1. FTIR
(KBr windows, C6D6 solution): 2118 cm-1. Anal. Calcd for
C25H25N: C, 88.45; H, 7.42; N, 4.13. Found: C, 88.43; H, 7.54; N,
4.17.
Synthesis of (µ-Cl)2[Cu(THF)(CNArMes2)]2. To a THF slurry
of cuprous chloride (0.036 g, 0.37 mmol, 2 mL) was added a THF
solution of CNArMes2 (0.125 g, 0.37 mmol, 3 mL). The mixture
was stirred for 2 h before all volatile materials were removed under
reduced pressure. Dissolution of the resulting colorless residue in
9018 Inorganic Chemistry, Vol. 47, No. 19, 2008

Cu(I) Complexes Featuring m-Terphenyl Isocyanides
THF (2-3 mL) followed by filtration and storage at -35 °C for
12 h resulted in colorless crystals, which were collected and dried
in vacuo. Yield: 0.210 g, 0.48 mmol, 81.3%. The coordinated THF
ligands are observed to dissociate in C6D6 solution. 1H NMR (500.3
MHz, C6D6, 20 °C): δ ) 6.90 (t, 1H, J ) 8 Hz, p-Ph), 6.84 (s, 4H,
m-Mes), 6.75 (d, 2H, J ) 8 Hz, m-Ph), 2.18 (s, 6H, p-CH3), 1.94
(s, 12H, o-CH3) ppm. 13C{1H} NMR (100.6 MHz, C6D6, 20 °C):
δ ) 148.9 (Ct N), 140.3, 138.4, 135.3, 133.7, 129.7, 129.4, 129.2,
at -35 °C for 36 h resulted in colorless crystals, which were
collected and dried in vacuo. Yield: 0.377 g, 0.48 mmol, 65.8%.
1H NMR (500.3 MHz, C6D6, 20 °C): δ ) 6.92 (t, 2H, J ) 8 Hz,
p-PH), 6.82 (s, 8H, m-Mes), 6.80 (d, 4H, J ) 8 Hz, m-Ph), 2.19 (s,
12H, p-CH3), 2.01 (s, 24H, o-CH3) ppm. 13C{1H} NMR (100.6
MHz, CDCl3, 20 °C): δ ) 147.9 (Ct N), 139.6, 138.2, 135.4, 133.2,
130.3, 129.8, 128.8, 125.2, 21.3 (p-CH3), 20.2 (o-CH3) ppm. FTIR
(KBr pellets): (νCN) 2143 cm-1 also 2946, 2919, 2860, 1612, 1460,
1271, 1223, 1147, 1031, 852, 756, 637 cm-1. FTIR (KBr windows,
C6D6 solution): (νCN) 2138 cm-1. Anal. Calcd for C50H50N2CuCl:
C, 77.20; H, 6.48; N, 3.60. Found: C, 76.90; H, 6.31; N, 3.42.
Synthesis of ICu(CNArMes2)3. To a THF slurry of cuprous iodide
(0.037 g, 0.20 mmol, 2 mL) was added a THF solution of CNArMes2
(0.200 g, 0.59 mmol, 3.0 equiv, 5 mL). The reaction was stirred
for about 2 h before volatile materials were removed under reduced
pressure. Dissolution of the resulting colorless residue in THF (5
mL) followed by filtration and storage at -35 °C for 48 h resulted
in colorless crystals, which were collected and dried in vacuo. Yield:
126.6, 21.4 (p-CH3), 20.2 (o-CH3) ppm. FTIR (KBr pellets) (νCN
)
2143 cm-1 also 2947, 2917, 2856, 1613, 1456, 1376, 851, 805,
756 cm-1. Prolonged drying in vacuo resulted in an analytically
pure sample lacking coordinated THF. Anal. Calcd for
C25H25NCuCl: C, 68.48; H, 5.75; N, 3.19. Found: C, 68.48; H, 5.83;
N, 3.11. Addition of several drops of pyridine (py) to a saturated
THF solution of (µ-Cl)2[Cu(THF)(CNArMes2)]2, followed by storage
at -35 °C for 3 d, afforded diffraction quality crystals of
(µ-Cl)2[Cu(py)(CNArMes2)]2. Prolonged drying of (µ-Cl)2[Cu-
(py)(CNArMes2)]2 in vacuo resulted in the removal of coordinated
pyridine.
1
0.170 g, 0.14 mmol, 70.3%. H NMR (500.3 MHz, C6D6, 20 °C):
Synthesis of (µ-Br)2[Cu(THF)(CNArMes2)]2. To a THF slurry
of cuprous bromide (0.085 g, 0.59 mmol, 3 mL) was added a THF
solution of CNArMes2 (0.200 g, 0.59 mmol, 1 equiv, 5 mL). The
reaction mixture was allowed to stir for 1 h, after which all volatile
materials were removed under reduced pressure. Dissolution of the
resulting colorless residue in THF (3-4 mL) followed by filtration
and storage at -35 °C for 48 h resulted in colorless crystals, which
were collected and dried in vacuo. Yield: 0.133 g, 0.28 mmol,
46.8%. The coordinated THF ligands are observed to dissociate in
δ ) 6.92 (t, 3H, J ) 8 Hz, p-Ph), 6.85 (s, 12H, m-Mes), 6.80 (d,
6H, J ) 8 Hz, m-Ph), 2.20 (s, 18H, p-CH3), 2.03 (s, 36H, o-CH3)
ppm. 13C{1H} NMR (100.6 MHz, C6D6, 20 °C): δ ) 139.8, 137.7,
135.8, 134.1, 129.7, 129.4, 129.2, 126.8, 21.4 (p-CH3), 20.6 (o-
CH3) ppm. FTIR (KBr pellets) (νCN) 2119 cm-1 also 2946, 2918,
2858, 1613, 1457, 1415, 1378, 1060, 1032, 850, 805, 756 cm-1
.
Anal. Calcd for C75H75N3CuI: C, 74.52; H, 6.25; N, 3.48. Found:
C, 73.48; H, 6.31; N, 3.42.
Synthesis of [(THF)Cu(CNArMes2)3]OTf. To a THF solution
of (C6H6)[CuOTf]2 (0.200 g, 0.40 mmol, 3 mL) was added a THF
solution of CNArMes2 (0.820 g, 2.42 mmol, 6 equiv, 10 mL). The
reaction mixture was allowed to stir for 1 h, after which all volatile
materials were removed under reduced pressure. Dissolution of the
resulting colorless residue in THF (5 mL) followed by filtration
and storage at -35 °C for 12 h resulted in colorless crystals, which
were collected and dried in vacuo. Yield: 0.749 g, 0.61 mmol,
76.4% in 4 crops. 1H NMR (400.1 MHz, CDCl3, 20 °C): δ ) 7.66
(t, 3H, J ) 8 Hz, p-Ph), 7.25 (d, 6H, J ) 8 Hz, m-Ph), 6.83 (s,
12H, m-Mes), 2.23 (s, 18H, p-CH3), 1.89 (s, 36H, o-CH3) ppm.
13C{1H} NMR (100.6 MHz, CDCl3, 20 °C): δ ) 146.0 (Ct N),
139.7, 138.3, 135.5, 133.1, 131.8, 130.3, 128.7, 124.0, 21.2 (p-
CH3), 20.1 (o-CH3) ppm. 19F{1H} NMR (282.3 MHz, CDCl3, 20
°C): δ ) -78.9 ppm. FTIR (KBr pellets) (νCN) 2160 cm-1 also
2946, 2919, 2860, 1612, 1460, 1271, 1223, 1147, 1031, 852, 756,
637 cm-1. Prolonged drying in vacuo did not remove the coordi-
nated molecule of THF. Anal. Calcd for C80H83F3N3O4SCu: C,
73.73; H, 6.42; N, 3.22. Found: C, 73.46; H, 6.60; N, 3.00. Crystals
of [(η1-C-C6H6)Cu(CNArMes2)3]OTf were obtained by slurrying
[(THF)Cu(CNArMes2)3]OTf in C6H6, removing all volatile materials
in vacuo and then allowing a dilute C6H6 solution of the resulting
colorless residue to stand at room temperature for several days.
1
C6D6 solution. H NMR (500.3 MHz, C6D6, 20 °C): δ ) 6.91 (t,
1H, J ) 7 Hz, p-Ph), 6.85 (s, 4H, m-Mes), 6.78 (d, 2H, m-Ph),
2.20 (s, 6H, p-CH3), 1.99 (s, 12H, o-CH3) ppm. 13C{1H} NMR
(100.6 MHz, CDCl3, 20 °C): δ ) 149.4 (Ct N), 140.3, 138.3, 135.3,
133.7, 129.7, 129.4, 129.3, 126.7, 21.5 (p-CH3), 20.4 (o-CH3) ppm.
FTIR (KBr pellet) (νCN) 2139 cm-1 also 2946, 2917, 2856, 1613,
1457, 1414, 1377, 1032, 849, 805, 757 cm-1. Prolonged drying in
vacuo resulted in an analytically pure sample lacking coordinated
THF. Anal. Calcd for C25H25NCuBr: C, 62.18; H, 5.22; N, 2.90.
Found: C, 61.01; H, 5.26; N, 2.76.
Synthesis of (µ-I)2[Cu(THF)(CNArMes2)]2. To a THF slurry of
cuprous iodide (0.112 g, 0.59 mmol, 5 mL) was added a THF
solution of CNArMes2 (0.200 g, 0.59 mmol, 1 equiv, 5 mL). The
reaction was stirred overnight before volatile materials were
removed under reduced pressure. Dissolution of the resulting
colorless residue in THF (5 mL) followed by filtration and storage
at -35 °C for 60 h resulted in colorless crystals, which were
collected and dried in vacuo. Yield: 0.178 g, 0.34 mmol, 57.0%.
The coordinated THF ligands are observed to dissociate in C6D6
1
solution. H NMR (500.3 MHz, C6D6, 20 °C): δ ) 6.91 (t, 1H, J
) 8 Hz, p-Ph), 6.88 (s, 4H, m-Mes), 6.80 (d, 2H, J ) 8 Hz, m-Ph),
2.25 (s, 6H, p-CH3), 2.02 (s, 12H, o-CH3) ppm. 13C{1H} NMR
(100.6 MHz, C6D6, 20 °C): δ ) 148.7 (Ct N), 140.3, 138.1, 135.5,
133.7, 129.7, 129.4, 129.3, 126.5, 21.6 (p-CH3), 20.5 (o-CH3) ppm.
FTIR (KBr pellets): (νCN) 2146 cm-1 also 2945, 2916, 2855, 1612,
1456, 1414, 1376, 1031, 848, 806, 757 cm-1. Prolonged drying in
vacuo resulted in an analytically pure sample lacking coordinated
THF. Anal. Calcd for C25H25NCuI: C, 56.66; H, 4.76; N, 2.64.
Found: C, 56.39; H, 4.79; N, 2.46.
Synthesis of CuCl(CNArMes2)2 from [(THF)Cu(CNArMes2)3]-
OTf and External Chloride Sources. (A) From LiCl: A THF
solution of [(THF)Cu(CNArMes2)3]OTf (0.028 g, 0.022 mmol, 2 mL)
was added to a THF slurry of LiCl (0.005 g, 0.11 mmol, 5.0 equiv).
The reaction mixture was stirred overnight and then all volatile
materials were removed under reduced pressure. The resulting
residue was subjected to two cycles of slurrying in Et2O (2 mL)
followed by evaporation. The mixture was then stirred for 2 h in
C6D6 and filtered. Analysis by 1H NMR spectroscopy (300.1 MHz)
resulted in a spectrum identical to that obtained by addition of 1.0
equiv of CNArMes2 to pure CuCl(CNArMes2)2.61 Analysis of the
Synthesis of ClCu(CNArMes2)2. To a CH2Cl2 solution of cuprous
chloride (0.073 g, 0.74 mmol, 2 mL) was added a CH2Cl2 solution
of CNArMes2 (0.500 g, 1.47 mmol, 2 equiv, 10 mL). The reaction
mixture was allowed to stir for 1 h, after which all volatile materials
were removed under reduced pressure. Dissolution of the resulting
colorless residue in CH2Cl (5 mL) followed by filtration and storage
(61) See Supporting Information.
Inorganic Chemistry, Vol. 47, No. 19, 2008 9019

Fox et al.
mixture by 19F{1H} NMR spectroscopy did not give rise to any
signal. A solution FTIR spectrum acquired on the sample exclu-
sively revealed resolved stretches attributable to both CNArMes2
(2118 cm-1) and CuCl(CNArMes2)2 (2138 cm-1). (B) From [NBu4]Cl:
A THF solution of [(THF)Cu(CNArMes2)3]OTf (0.020 g, 0.016
mmol) was added to a THF solution of [NBu4]Cl (0.004 g, 0.015
mmol. 1.0 equiv). The reaction mixture was stirred overnight and
then all volatile materials were removed under reduced pressure.
The resulting residue was subjected to two cycles of slurrying in
n-pentane (2 mL) followed by evaporation. The mixture was then
stirred for 2 h in C6D6 and filtered. Spectroscopic analysis was
identical to that described for treatment of [(THF)Cu-
(CNArMes2)3]OTf with LiCl.61
Crystallographic Structure Determinations. Single-crystal
X-ray structure determinations were carried out at 100(2) K on
either a Bruker P4 or Platform Diffractometer equipped with a
Bruker APEX detector. Mo KR radiation (λ ) 0.71073 Å) was
used in all cases. All structures were solved by direct methods with
SIR 200462 and refined by full-matrix least-squares procedures
utilizing SHELXL-97.63 The crystallographic routine SQUEEZE64
was used to account for disordered THF molecules of co-
crystallization in the structures of (µ-Cl)2[Cu(THF)(CNArMes2)]2,
(µ-Br)2[Cu(THF)(CNArMes2)]2 and ICu(CNArMes2)3. Crystallo-
graphic data collection and refinement information are listed in
Table 2.
version 2007.01.67 For all atoms, the triple-ꢁ Slater-type orbital
TZ2P ADF basis set was utilized without frozen cores. Relativistic
effects were included by use of the zero-order regular approximation
(ZORA).68,69 The local density approximation of Vosko et al.70
(VWN) was coupled with the generalized gradient approximation
corrections described by Becke71 and Perdew72,73 for electron
exchange and correlation, respectively. Crystallographic atomic
coordinates were used as input where appropriate. Optimized
geometries and molecular orbitals were visualized with the ADF-
View graphical routine of the ADF-GUI.74
Acknowledgment. We gratefully acknowledge the UCSD
Department of Chemistry and Biochemistry and the Camille
and Henry Dreyfus New Faculty Awards Program for
generous financial support. Professors Clifford P. Kubiak and
Christopher C. Cummins are thanked for invaluable discus-
sions.
1
Supporting Information Available: Representative H NMR
and FTIR spectra for exchange reactions, results of computational
studies and crystallographic information files (CIF). This material
is available free of charge via the Internet at http://pubs.acs.org.
IC8010986
Computational Details. DFT calculations were performed with
(67) ADF 2007.01; SCM, Theoretical Chemistry, Vrije Universiteit:
Amsterdam, The Netherlands; www.scm.com. Access date, October,
2007.
the Amsterdam Density Functional (ADF) program suite,65,66
(68) van Lenthe, E.; Baerends, E. J.; Snijders, J. G. J. Chem. Phys. 1993,
99, 4597–4610.
(69) van Lenthe, E.; Snijders, J. G.; Baerends, E. J. J. Chem. Phys. 1996,
105, 6505–6516.
(62) Burla, M. C.; Caliandro, R.; Camalli, M.; Carrozzini, B.; Cascarano,
G. L.; De Caro, L.; Gaicovazzo, C.; Polidori, G.; Spagna, R. J. Appl.
Crystallogr. 2005, 38, 381–388.
(63) Sheldrick, G. M. Acta Crystallogr. 2008, A64, 112–122.
(64) van der Sluis, P.; Spek, A. L. Acta Crystallogr. 1990, A46, 194–201.
(65) te Velde, G.; Bickelhaupt, F. M.; Baerends, E. J.; Fonseca Guerra,
C.; van Gisbergen, S. J. A.; Snijders, J. G.; Ziegler, T. J. Comput.
Chem. 2001, 22, 931–967.
(66) Fonseca Guerra, C.; Snijders, J. G.; te Velde, G.; Baerends, E. J. Theor.
Chem. Acc. 1998, 99, 391–403.
(70) Vosko, S. H.; Wilk, L.; Nusair, M. Can. J. Phys 1980, 58, 1200–
1211.
(71) Becke, A. D. Phys. ReV. A 1988, 38, 3098–3100.
(72) Perdew, J. P. Phys. ReV. B 1986, 33, 8822–8824.
(73) Perdew, J. P. Phys. ReV. B 1986, 34, 7406–7406; Erratum.
(74) ADF-GUI 2007.01; SCM: Amsterdam, The Netherlands; www.scm.
com. Access date, February, 2008.
9020 Inorganic Chemistry, Vol. 47, No. 19, 2008