Structural and spectroscopic studies of three-coordinate copper(I) supported by bis(phosphino)borate ligands

Article abstract of DOI:10.1016/j.poly.2004.08.008

Monoanionic and neutral three-coordinate complexes of copper(I) have been prepared using several bis(phosphino)borate ligands. Substitution of a labile acetonitrile ligand in [(3,5-Me₂Ph)₂B(CH₂P ^tBu₂)

Full text of DOI:10.1016/j.poly.2004.08.008

Polyhedron 23 (2004) 2901–2913
www.elsevier.com/locate/poly
Structural and spectroscopic studies of three-coordinate
copper(I) supported by bis(phosphino)borate ligands
*
J. Christopher Thomas, Jonas C. Peters
Contribution from the Division of Chemistry and Chemical Engineering, Arnold and Mabel Beckman Laboratories of Chemical Synthesis,
California Institute of Technology, Pasadena, CA 91125, USA
Received 1 July 2004; accepted 25 August 2004
Available online 28 October 2004
Dedicated to Professor Malcolm H. Green, an inspiring organometallic chemist
Abstract
The bis(phosphino)borates [(p-tBuPh)2B(CH2PPh2)2][ASN] (1[ASN]; ASN = 5-azonia-spiro[4.4]nonane), [Ph2B(CH2PiPr2)2]-
Li(THF)2 (2[Li]), and [(3,5-Me2Ph)2B(CH2PtBu2)2]ꢀ (3[Li] and 3[Tl]) react with copper(I) reagents to generate anionic and neutral
complexes. Reaction of 1[ASN] with CuI provides the 1:1 adduct [[(p-tBuPh)2B(CH2PPh2)2]CuI][ASN] (4). CuCl reacts with 3[Li] in
THF to afford [[(3,5-Me2Ph)2B(CH2PtBu2)2]CuCl][Li(THF)4] (5), along with a minor byproduct, the three-coordinate bis(phos-
phine) adduct {(3,5-Me2Ph)B(CH2PtBu2)2}CuCl (6). An analogous neutral complex, {PhB(CH2PtBu2)2}CuCl (7), can be synthe-
sized directly by reacting CuCl with the neutral phosphino borane PhB(CH2PtBu2)2. Reaction of the substituted copper(I) halide
Me2S Æ CuBr with 3[Tl] provides the anionic dimer complex [{[(3,5-Me2Ph)2B(CH2PtBu2)2]Cu}2(l-Br)]Tl (8). The neutral solvent
adducts [Ph2B(CH2PiPr2)2]Cu(NCCH3) (9) and [(3,5-Me2Ph)2B(CH2PtBu2)2]Cu(NCCH3) (10) are prepared by the reactions
between [Cu(CH3CN)4][PF6] and 2[Li] or 3[Li], respectively. Neutral 10 is a useful precursor to several other neutral species via sub-
stitution of the labile acetonitrile ligand, including [(3,5-Me2Ph)2B(CH2PtBu2)2]Cu(PMe2Ph)(11), [(3,5-Me2Ph)2B(CH2PtBu2)2]-
Cu(S@PMe3) (12), [(3,5-Me2Ph)2B(CH2PtBu2)2] Cu(2,6-lutidine) (13), and [(3,5-Me2Ph)2B(CH2PtBu2)2]Cu(CNtBu) (14). Attempts
to isolate a neutral monocarbonyl adduct, [(3,5-Me2Ph)2B(CH2PtBu2)2]Cu(CO) (15), are frustrated by the high lability of the CO
ligand. The solid-state crystal structures of complexes 6, 8, 9, 10, and 11 have been determined and are described.
ꢀ 2004 Elsevier Ltd. All rights reserved.
Keywords: Zwitterions; Monoanionic ligands; Phosphines; Syntheses; Structures; Boron
1. Introduction
control both steric and electronic factors that dictate
overall reactivity profiles. These include modified
bis- and tris(pyrazolyl)borates [4], b-diketiminates [5],
N-heterocyclic carbenes [6], and a host of other nitroge-
nous ligands [7].
We recently reported the synthesis of a new family of
bis(phosphino)borate ligands that are both sterically
and electronically tunable [8]. These ligands are anionic
relatives to the better known bis(pyrazolyl)borate and
b-diketiminate ligands, and their fundamental coordi-
nation chemistry is therefore of comparative interest.
In this contribution, we introduce a series of well-
defined copper(I) complexes supported by monoanionic
Copper(I) complexes play a significant role in many
catalytic and stoichiometric processes, including cata-
lytic hydrocarbon functionalization reactions [1], cata-
lytic oxidation reactions [2], and biomimetic dioxygen
activation [3]. Several well-defined copper(I) systems
have been developed recently using ligands designed to
*
Corresponding author. Tel.: +1 626 395 4036; fax: +1 626 577
4088.
E-mail address: jpeters@caltech.edu (J.C. Peters).
0277-5387/$ - see front matter ꢀ 2004 Elsevier Ltd. All rights reserved.
doi:10.1016/j.poly.2004.08.008

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J. Christopher Thomas, J.C. Peters / Polyhedron 23 (2004) 2901–2913
1
sion of LiCH2PtBu2.
All other reagents were
purchased from commercial vendors and used without
further purification.
2.2. Syntheses of complexes
2.2.1. [[(p-tBuPh)2B(CH2PPh2)2]CuI][ASN] (4)
Solid CuI (83.6 mg, 439 lmol) and [(p-tBuPh)2
B(CH2PPh2)2][ASN] (351.8 mg, 438.7 lmol) were com-
bined with THF (4 mL) and ethanol (0.3 mL). The reac-
tion mixture was stirred for 2.5 h. Volatiles were
removed under reduced pressure. The resulting solids
were washed with diethyl ether (3 mL) and dried under
reduced pressure, providing analytically pure white 4
1
(432.8 mg, 99.4%). H NMR (300 MHz, acetone-d6): d
7.60 (m, 8H), 7.12 (m, 16H), 6.82 (d, 4H), 3.69 (m,
8H), 2.24 (m, 8H), 1.76 (br, 4H), 1.21 (s, 16H).
13C{1H} NMR (75.4 MHz, acetone-d6): d 162.7 (br),
1
144.55, 141.80 (d, JP–C = 12.3 Hz), 141.64 (d,
2
1JP–C = 12.3 Hz), 133.83, 133.71 (d, JP–C = 8.0 Hz),
Fig. 1. Bis(phosphino)borate ligands used to prepare copper(I)
complexes.
2
133.60 (d, JP–C = 8.0 Hz), 128.72, 128.49 (d,
3
3JP–C = 4.3 Hz), 128.43 (d, JP–C = 4.0 Hz), 123.51,
1
63.78 (t, (CH2CH2)2N, JN–C = 3.4 Hz), 34.42 (Ph-
bis(phosphino)borates. The aim of this initial study is
to develop reliable protocols for the generation and iso-
lation of these new copper species, to establish their
structural characterization, and to assess their ligand
substitution chemistry. In this context, we examine
the copper(I) coordination chemistry of the three
bis(phosphino)borate ligands: [(p-tBuPh)2B(CH2P-
Ph2)2][ASN] (1[ASN]), [Ph2B(CH2PiPr2)2]Li(THF)2
(2[Li]), and [(3,5-Me2Ph)2B(CH2PtBu2)2]ꢀ (3[Li] and
3[Tl]) (Fig. 1). In particular, we emphasize the use of
the sterically encumbered tert-butyl phosphine ligand
3 due to its ability to enforce three-coordinate geome-
tries for a host of copper(I) complexes. Our hope is that
the complexes described will serve as useful
‘‘[BP2]CuI(L)’’ sources in the context of future group
transfer studies.
C(CH3)3), 32.15 (Ph-C(CH3)3), 22.84 ((CH2CH2)2N),
22.0 (br, B(CH2PPh2)2). 31P{1H} NMR (121.4 MHz,
acetone-d6): d ꢀ13.08. 11B{1H} NMR (128.3 MHz,
acetone-d6): d ꢀ12.5. Anal. Calc. for C54H66BCuINP2:
C, 65.36; H, 6.70; N, 1.41. Found: C, 65.08; H, 6.94;
N, 1.21%.
2.2.2. [[(3,5-Me2Ph)2B(CH2PtBu2)2]CuCl][Li(THF)4]
(5)
Solid CuCl (26.5 mg, 268 lmol) was suspended in
THF (1.5 mL), stirred vigorously, and a THF solution
(4 mL) of [(3,5-Me2Ph)2B(CH2PtBu2)2]Li(OEt2) (166.2
mg, 268.2 lmol) was then added to the stirring suspen-
sion. After stirring for 24 h, analysis by 31P{1H}
NMR spectroscopy revealed the formation of one major
product, along with two minor byproducts. The reaction
mixture was then filtered. The resulting filtrate was con-
centrated under reduced pressure to 0.5 mL. Vapor dif-
fusion of petroleum ether into the THF solution
provided white crystalline solids over several days. The
isolated solids were dried under reduced pressure to pro-
vide the major product, [[(3,5-Me2Ph)2B(CH2PtBu2)2]-
CuCl][Li(THF)4] (163.9 mg, 65.5%). 1H NMR (300
MHz, C6D6/THF-d8, 6:1): d 7.59 (s, 4H, ortho-
2. Experimental
2.1. General considerations
General procedures were performed according to pre-
viously published methods [9]. The compounds
[(p-tBuPh)2B(CH2PPh2)2][ASN]
(1[ASN]),
[Ph2B
(CH2PiPr2)2]Li(THF)2 (2[Li]), [(3,5-Me2Ph)2B(CH2Pt-
Bu2)2]Li(OEt2) (3[Li]), [(3,5-Me2Ph)2B(CH2PtBu2)2]Tl
(3[Tl]), and Me3P@S were prepared by published meth-
ods [8]. BuNC was distilled under dinitrogen and dried
˚
over 3 A molecular sieves prior to use. 2,6-Lutidine was
sparged with dinitrogen and then dried with CaH2 and
distilled under dinitrogen. PhB(CH2PtBu2)2 was gener-
ated by the addition of PhBCl2 to a cold ethereal suspen-
1
The synthesis of PhB(CH2PtBu2)2 and its use as a ligand building
block to other borate ligands will be reported separately (C.M.
Thomas, J.C. Peters, manuscript in preparation). Key characterization
data for PhB(CH2PtBu2)2: 1H NMR (300 MHz, C6D6): d = 8.02 (m,
t
2
2H, o-Ph), 7.27 (m, 3H, m, p-Ph), 2.27 (d, JP–H = 5.7 Hz, CH2), 1.12
2
t
(d, JP–H = 10.5 Hz, 36 H, Bu). 31P NMR (300 MHz, C6D6): d = 38.4
(s). Anal. Calc. for C24H45BP2: C, 70.93; H, 11.16. Found: C, 69.32; H,
10.60%.

J. Christopher Thomas, J.C. Peters / Polyhedron 23 (2004) 2901–2913
2903
(Me2C6H3)2B), 6.62 (s, 2H, para-(Me2C6H3)2B), 3.54
(m, 16H, (CH2CH2)2O) 2.29 (s, 12H, ((CH3)2C6H3)2B),
1.92 (br, 4H, B(CH2PtBu2)2), 1.45 (m, 16H,
solution. The solution was filtered, and volatiles were re-
moved under reduced pressure, forming microcrystalline
yellow {PhB(CH2PtBu2)2}CuCl (30.7 mg, 97.2%). 1H
NMR (300 MHz, C6D6): d 7.88 (m, 2H), 7.28 (m, 3H),
1.73 (br, 4H, B(CH2PtBu)2), 1.22 (d, 18H, P(C(CH3)3)2,
3
(CH2CH2)2O) 1.32 (d, 18H, P(C(CH3)3)2, JP–H = 5.7
3
Hz), 1.30 (d, 18H, P(C(CH3)3)2, JP–H = 6.3 Hz).
13C{1H} NMR (75.4 MHz, C6D6/THF-d8, 6:1): d
3
3JP–H = 6.3 Hz), 1.20 (d, 18H, P(C(CH3)3)2, JP–
167.3
(br,
ipso-(Me2C6H3)2B),
134.52
(meta-
H = 6.6 Hz). 13C{1H} NMR (75.4 MHz, C6D6): d
134.60, 133.29, 129.05, 34.47 (m, CH2P(C(CH3)3)2),
29.82 (m, CH2P(C(CH3)3)2), 18.8 (br, BC H2P).
31P{1H} NMR (121.4 MHz, C6D6): d 23.11. 11B{1H}
NMR (160.4 MHz, C6D6): d 75.2. Anal. Calc. for
C24H45BClCuP2: C, 57.04; H, 8.98. Found: C, 57.40;
H, 8.67%.
(Me2C6H3)2B), 131.89 (ortho-(Me2C6H3)2B), 124.50
(para-(Me2C6H3)2B), 68.17 ((CH2C H2)2O), 34.22 (d,
CH2P(C(CH3)3)2,
CH2P(C(CH3)3)2,
CH2P(C(CH3)3)2), 30.92 (br, CH2P(C(CH3)3)2), 26.17
((C H2CH2)2O), 22.68 (((CH3)2C6H3)2B), 14.7 (br, BC
H2P). 31P{1H} NMR (121.4 MHz, C6D6/THF-d8, 6:1):
d 33.31. 11B{1H} NMR (128.3 MHz, C6D6/THF-d8,
6:1): d ꢀ14.0. Anal. Calc. for C50H90BClCuLiO4P2: C,
64.38; H, 9.71. Found: C, 64.30; H, 9.70%.
1JP-C = 4.6
1JP–C = 4.6
Hz),
Hz),
34.16
31.05
(d,
(br,
2.2.5. [{[(3,5-Me2Ph)2B(CH2PtBu2)2]Cu}2(l-Br)]Tl
(8)
Solid Me2S Æ CuBr (16.2 mg, 78.8 lmol) was sus-
pended in THF (3 mL). While stirring, a THF solution
(9 mL) of [(3,5-Me2Ph)2B(CH2PtBu2)2]Tl (58.6 mg, 78.8
lmol) was added dropwise. Upon completing the addi-
tion, the reaction mixture was stirred for 15 min. The
reaction mixture was filtered, removing white and gray
solids. The resulting solution was concentrated under re-
duced pressure to 1 mL. Vapor diffusion of petroleum
ether into the THF solution provided colorless crystals
over several days. The crystals were dried under reduced
2.2.3. {(3,5-Me2Ph)B(CH2PtBu2)2}CuCl (6)
Yellow crystals of the minor byproduct, 6, were iso-
lated from a separate reaction, carried-out in an analo-
gous fashion to that used in the preparation of 5, by
petroleum ether diffusion into a THF solution of the
crude reaction mixture. A 31P{1H} NMR spectrum of
the solution prior to crystallization showed 6 to be pre-
sent as approximately 15% of the observed diamagnetic
phosphorus containing products. 31P{1H} NMR (121.4
MHz, THF): d 23.75. The identity of 6 was established
by XRD analysis (see Fig. 2), and by comparison to
the spectral properties of independently prepared 7.
1
pressure to provide 8 (28.7 mg, 48.9%). H NMR (300
MHz, THF-d8): d 7.03 (s, 4H, ortho-(Me2C6H3)2B),
6.34 (s, 2H, para-(Me2C6H3)2B), 2.11 (s, 12H,
((CH3)2C6H3)2B), 1.53 (br, 4H, B(CH2PtBu)2), 1.12 (d,
3
18H, P(C(CH3)3)2, JP–H = 6.3 Hz), 1.10 (d, 18H,
3
2.2.4. {PhB(CH2PtBu2)2}CuCl (7)
P(C(CH3)3)2, JP–H = 6.0 Hz). 13C{1H} NMR (75.4
Solid PhB(CH2PtBu2)2 1 (25.4 mg, 62.5 lmol) and
CuCl (6.2 mg, 63 lmol) were combined in THF (4
mL) and stirred for 1 h, forming a homogeneous yellow
MHz, THF-d8): d 167 (br), 134.58, 131.50, 124.35,
34.34 (d, CH2P(C(CH3)3)2, JP–C = 6.0 Hz), 34.26 (d,
1
CH2P(C (CH3)3)2, 1JP–C = 6.4 Hz), 30.99 (d,
2
CH2P(C(CH3)3)2, JP–C = 4.8 Hz), 30.77 (d, CH2P(C(C
2
H3)3)2, JP–C = 3.7 Hz), 22.31 (((CH3)2C6H3 )2B), 14.8
(br, BC H2P). 31P{1H} NMR (121.4 MHz, THF-d8): d
38.79. 11B{1H} NMR (128.3 MHz, THF-d8): d ꢀ14.4.
Anal. Calc. for C68H116B2BrCu2P4Tl: C, 54.79; H,
7.84. Found: C, 55.17; H, 7.55%.
2.2.6. [Ph2B(CH2PiPr2)2]Cu(NCCH3) (9)
Solid [Ph2B(CH2PiPr2)2]Li(THF)2 (157.5 mg, 272.2
lmol) and solid [Cu(CH3CN)4][PF6] (101.5 mg, 272.3
lmol) were combined in Et2O (4 mL). The reaction mix-
ture was stirred for 30 min, forming a pale yellow solu-
tion. Volatiles were removed under reduced pressure,
providing pale yellow solids. The solids were washed
with acetonitrile (3 · 0.5 mL). The resulting solids were
dissolved in THF (3 mL) and filtered. Removal of vola-
tiles under reduced pressure provided white solids that
analyzed as [Ph2B(CH2PiPr2)2]Cu(NCCH ) (62.7 mg,
Fig. 2. Displacement ellipsoid representation (50%) of {(3,5-
Me2Ph)B(CH2PtBu2)2}CuCl (6). Hydrogen atoms are omitted for
3
43.3%). Crystals for an X-ray diffraction experiment
were grown by vapor diffusion of petroleum ether into
˚
clarity. Selected interatomic distances (A) and angles (ꢁ): P1–Cu,
2.2433(11); P2–Cu, 2.2481(12); Cl–Cu, 2.2183(12); B–Cu, 3.639(5); P1–
Cu–P2, 108.55(5); P1–Cu–Cl, 129.28(5); P2–Cu–Cl, 121.93(5).
1
a THF solution of 9. H NMR (300 MHz, THF-d8): d

2904
J. Christopher Thomas, J.C. Peters / Polyhedron 23 (2004) 2901–2913
3
7.30 (br, 4H), 6.90 (t, 4H, JH–H = 7.2 Hz), 6.72 (t, 2H,
6.9 Hz), 2.206 (s, 3H, CH3CN), 1.73 (m, 4H,
P(CH(CH3)2)2), 1.21 (br, 4H, BCH2P), 1.07 (dd, 12H,
P(CH(CH3)2)2, J = 7.2, 15 Hz), 0.87 (dd, 12H,
P(CH(CH3)2)2, J = 6.9, 13.2 Hz). 13C{1H} NMR (75.4
MHz, THF-d8): d 166 (br), 133.55, 126.84, 124.24
(CH3CN), 123.88, 21.6 (m, P(CH(CH3)2)), 19.34
(m, 5H, P(C6H5)), 6.74 (s, 2H, para-(Me2C6H3)2B),
2.37 (s, 12H, ((CH3)2C6H3)2B), 1.93 (br, 4H,
B(CH2PtBu)2), 1.07 (m, 42H, P(C(CH3)3)2 and
P(CH3)2). 13C{1H} NMR (125.7 MHz, C6D6): d
1
166.85 (q, JB–C = 54 Hz), 135.33, 131.72, 130.65 (d,
JP–C = 12 Hz), 130.12, 129.48 (d, JP–C = 8.3 Hz),
1
125.30, 34.38 (d, P(C(CH3)3)2, JP–C = 6.0 Hz), 34.30
1
P(CH(CH3)2), 17.10 (q, BCH2P, JB–C = 41 Hz), 1.52
(d, P(C(CH3)3)2, 1JP–C = 6.0 Hz), 31.04 (d,
(CH3CN). 31P{1H} NMR (121.4 MHz, THF-d8): d
17.83. 11B{1H} NMR (160.4 MHz, THF-d8): d ꢀ14.4.
IR: (KBr (s), cmꢀ1) mCN = 2265 (w). Anal. Calc. for
C28H45BCuNP2: C, 63.22; H, 8.53; N, 2.63. Found: C,
63.27; H, 8.73, N, 2.84%.
2
P(C(CH3)3)2, JP–C = 4.1 Hz), 30.99 (d, P(C(CH3)3)2,
2JP–C = 4.0 Hz), 22.99 (((CH3)2C6H3)2B), 15.49 (d,
1
P(CH3)2, JP–C = 18 Hz), 14.09 (br q, B(CH2PtBu)2,
1JB–C = 43 Hz). 31P{1H} NMR (121.4 MHz, C6D6): d
2
40.81 (d, 2P, CH2PtBu2, JP-P = 79 Hz), ꢀ36.22 (t, 1P,
2
P Me2Ph, JP–P = 79 Hz). 11B{1H} NMR (128.3 MHz,
2.2.7. [(3,5-Me2Ph)2B(CH2PtBu2)2]Cu(NCCH3) (10)
White [(3,5-Me2Ph)2B(CH2PtBu2)2]Li(OEt2) (323.1
mg, 521.4 lmol) and [Cu(CH3CN)4][PF6] (194.4 mg,
521.6 lmol) were combined, and diethyl ether (10 mL)
was added. The reaction mixture was stirred vigorously
for 40 min. Volatiles were removed under reduced pres-
sure, providing pale yellow solids. The solids were
washed with acetonitrile (3 · 0.8 mL), and then dis-
solved in THF (5 mL) and filtered. The resulting solu-
tion was concentrated to dryness under reduced
pressure, providing fine white, analytically pure 10
(280.8 mg, 83.6%). Crystals of 10 were grown by vapor
diffusion of petroleum ether into a THF solution of 10.
1H NMR (300 MHz, THF-d8): d 7.01 (s, 4H, ortho-
(Me2C6H3)2B), 6.33 (s, 2H, para-(Me2C6H3)2B), 2.28
(s, 3H, Cu-NCCH3), 2.11 (s, 12H, ((CH3)2C6H3)2B),
1.51 (br s, 4H, B(CH2PtBu)2), 1.12 (d, 18H,
P(C(CH3)3)2), 1.10 (d, 18H, P(C(CH3)3)2). 13C{1H}
C6D6): d ꢀ14.4. Anal. Calc. for C42H69BCuP3: C,
68.05; H, 9.38. Found: C, 67.87; H, 9.17%.
2.2.9. [(3,5-Me2Ph)2B(CH2PtBu2)2]Cu(S = PMe3) (12)
Solid Me3P = S (8.8 mg, 81 lmol) and 10 (52.1 mg,
80.9 lmol) were dissolved in THF (2 mL). After 15
min, the reaction mixture was filtered and concentrated
to dryness under reduced pressure. The resulting white
solids were washed with petroleum ether (3 · 1 mL)
and dried under reduced pressure, producing analyti-
1
cally pure white 12 (49.2 mg, 85.6%). H NMR (300
MHz, C6D6): d 7.73 (s, 4H, ortho-(Me2C6H3)2B), 6.75
(s,
2H,
para-(Me2C6H3)2B),
2.39
(s,
12H,
((CH3)2C6H3)2B), 2.03 (br s, 4H, B(CH2PtBu)2), 1.29
(m, 36H, P(C(CH3)3)2), 0.90 (d, 9H, S@P(CH3)3,
2JP–H = 13 Hz). 13C{1H} NMR (75.4 MHz, C6D6): d
134.76, 131.33, 124.71, 34.10 (br, P(C(CH3)3)2), 30.64
1
(m, P(C(CH3)3)2), 30.25 (d, S = P(CH3)3, JP–C = 6.7
1
NMR (75.4 MHz, THF-d8): d 166.7 (br q, JB–C = 44
Hz), 134.43, 131.59, 124.87 (Cu-NCCH3), 124.27,
Hz), 22.47 (((CH3)2C6H3)2B). 31P{1H} NMR (121.4
MHz, C6D6): d 35.05 (s, 2P, CH2PtBu2), 26.48 (s, 1P,
S = P Me3). 11B{1H} NMR (128.3 MHz, C6D6): d
ꢀ14.3. Anal. Calc. for C37H67BCuP3S: C, 62.48; H,
9.49. Found: C, 62.28; H, 9.25%.
1
34.32 (d, P(C(CH3)3)2, JP–C = 6.0 Hz), 34.24 (d,
1
P(C(CH3)3)2, JP–C = 6.0 Hz), 30.85 (d, P(C(CH3)3)2,
2
2JP-C = 4.3 Hz), 30.79 (d, P(C(CH3)3)2, JP–C = 4.3
Hz), 22.34 ((CH3)2C6H3)2B, 14.22 (br q, B(CH2PtBu)2,
1JB–C = 42 Hz), 1.59 (Cu-NCCH3). 31P{1H} NMR
(121.4 MHz, THF-d8): d 36.4. 11B{1H} NMR (128.3
2.2.10. [(3,5-Me2Ph)2B(CH2PtBu2)2]Cu(2,6-lutidine)
(13)
MHz, THF-d8): d-14.2. IR: (KBr (s), cmꢀ1
)
CN = 2267 (w). Anal. Calc. for C36H61BCuNP2: C,
Solid 10 (51.7 mg, 80.3 lmol) was dissolved in THF
(2 mL). An aliquot of 2,6-lutidine (9.6 lL, 83 lmol)
was added to the reaction mixture, providing a pale yel-
low solution. After 15 min, the solution was concen-
trated to dryness under reduced pressure. The resulting
white solids were washed with petroleum ether (3 · 1
mL) and dried under reduced pressure, providing
m
67.12; H, 9.54; N, 2.17. Found: C, 66.98; H, 9.55; N,
2.43%.
2.2.8. [(3,5-Me2Ph)2B(CH2PtBu2)2]Cu(PMe2Ph) (11)
A THF solution (2 mL) of Me2PPh (12.8 lL, 90.0
lmol) was added to solid 10 (58.0 mg, 90.0 lmol), pro-
viding a colorless solution. After 15 min, the solution
was concentrated to dryness under reduced pressure.
The resulting white solids were washed with petroleum
ether (3 · 1 mL) and dried under reduced pressure, pro-
viding analytically pure white 11 (61.8 mg, 92.7%). Crys-
tals of 11 were grown by vapor diffusion of petroleum
1
analytically pure pale yellow 13 (48.9 mg, 85.8%). H
NMR (300 MHz, C6D6): d 7.67 (s, 4H, ortho-
(Me2C6H3)2B), 6.76 (t, 1H, para-Me2C5H3N,
3JH–H = 7.5 Hz), 6.75 (s, 2H, para-(Me2C6H3)2B), 6.32
3
(d, 2H, meta-Me2C5H3N, JH–H = 7.5 Hz), 2.50 (s, 6H,
(CH3)2C5H3N), 2.38 (s, 12H, ((CH3)2C6H3)2B), 1.99
(br s, 4H, B(CH2PtBu)2), 1.14 (d, 18H, P(C(CH3)3)2,
3JP–H = 5.7 Hz), 1.12 (d, 18H, P(C(CH3)3)2,
3JP–H = 6.3 Hz). 13C{1H} NMR (75.4 MHz, C6D6):
1
ether into a THF solution of 11. H NMR (300 MHz,
C6D6): d 7.68 (s, 4H, ortho-(Me2C6H3)2B), 6.96–7.14

J. Christopher Thomas, J.C. Peters / Polyhedron 23 (2004) 2901–2913
2905
d
125.33, 122.55, 34.17 (d, P(C(CH3)3)2, JP–C = 5.4 Hz),
166.2 (br), 156.98, 137.62, 135.12, 132.57,
1
31P{1H} NMR (121.4 MHz, THF-d8): d 42.33. 11B{1H}
NMR (128.3 MHz, THF-d8): d ꢀ13.9.
1
34.09 (d, P(C(CH3)3)2, JP–C = 5.7 Hz), 31.05 (d,
(b) In a 25 mL Schlenk flask, solid 10 (14.3 mg, 22.2
lmol) was dissolved in THF (1.5 mL) with a stirbar.
The solution was stirred under a stream of CO gas until
2
P(C(CH3)3)2, JP–C = 4.3 Hz), 31.00 (d, P(C(CH3)3)2,
2JP–C = 4.0 Hz), 26.70 (o,o-(CH3)2C5H5N), 22.97
1
1
(((CH3)2C6H3)2B), 14.88 (br q, B(CH2PtBu)2, JB–C
=
dry, producing pale green solids. H NMR (300 MHz,
40 Hz). 31P{1H} NMR (121.4 MHz, C6D6): d 36.10.
11B{1H} NMR (128.3 MHz, C6D6): d ꢀ14.1. Anal. Calc.
for C41H67BCuNP2: C, 69.33; H, 9.51; N, 1.97. Found:
C, 68.94; H, 9.14; N, 2.09%.
C6D6): d 7.56 (s, 4H, ortho-(Me2C6H3)2B), 6.72 (s, 2H,
para-(Me2C6H3)2B), 2.35 (s, 12H, ((CH3)2C6H3)2B),
1.86 (br, 4H, B(CH2PtBu)2), 1.07 (d, 18H, P(C(CH3)3)2,
3
3JP–H = 6.3 Hz), 1.12 (d, 18H, P(C(CH3)3)2, JP–H = 6.3
Hz). IR: (THF/KBr, cmꢀ1) mCO = 2084 (st).
2.2.11. [(3,5-Me2Ph)2B(CH2PtBu2)2]Cu(CNtBu) (14)
A THF solution (2 mL) of tert-butyl isonitrile (11.8
lL, 104 lmol) was added to solid 10 (66.3 mg, 103
lmol), providing a colorless solution. After 15 min,
the solution was concentrated to dryness under reduced
pressure. The resulting white solids were washed with
petroleum ether (3 · 1 mL) and dried under reduced
pressure, providing analytically pure white 14 (63.9
mg, 90.4%). 1H NMR (300 MHz, C6D6): d 7.68 (s,
4H, ortho-(Me2C6H3)2B), 6.74 (s, 2H, para-
(Me2C6H3)2B), 2.38 (s, 12H, ((CH3)2C6H3)2B), 1.94 (br
s, 4H, B(CH2PtBu)2), 1.24 (d, 18H, P(C(CH3)3)2,
3JP–H = 6.6 Hz), 1.22 (d, 18H, P(C(CH3)3)2,
3JP–H = 6.0 Hz), 0.77 (s, 9H, Cu-CNC(CH3)3).
13C{1H} NMR (75.4 MHz, C6D6): d 166.7 (br q,
1JB–C = 45 Hz), 144.26 (br, Cu-CNtBu), 135.25, 131.91,
125.30, 57.02 (Cu-CNC(CH3)3), 34.46 (d, P(C(CH3)3)2,
2.3. X-ray crystallography
The general X-ray experimental procedure was per-
formed according previously published methods
[9]. Crystallographic information is provided in Table 1.
The structures of 8 Æ THF Æ pentane and 10 Æ 0.56THF Æ
0.22 pentane contained sites of disordered solvent
molecules.
3. Results and discussion
3.1. Copper(I) complexes containing halides
The formation of low-coordinate copper complexes
using bis(phosphino)borate ligands was examined using
several Cu(II) precursors, such as CuCl2 Æ 0.8THF [10],
anhydrous Cu(OAc)2, and Cu(OTf)2. As has been ob-
served in previous efforts to develop Cu(II)–phosphine
chemistry [11], we found that Cu(II) was easily reduced
to Cu(I) in the presence these reducing phosphine ligands
to provide ill-defined degradation products. In compari-
son, copper(I) starting materials provide in many cases
clean 1:1 adducts with monoanionic bis(phosphino)bor-
ate ligands. Anionic complexes of copper(I) halides were
prepared using both the phenyl substituted phosphine
ligand [(p-tBuPh)2B(CH2PPh2)2] ꢀ (1) and the tert-butyl
1
1JP–C = 6.3 Hz), 34.38 (d, P(C(CH3)3)2, JP–C = 6.0
2
Hz), 30.97 (d, P(C(CH3)3)2, JP–C = 4.0 Hz), 30.92 (d,
2
P(C(CH3)3)2, JP–C = 4.0 Hz), 29.99 (Cu-CNC(CH3)3),
22.98 (((CH3)2C6H3)2B), 12.84 (br q, B(CH2PtBu)2,
1JB–C = 41 Hz). 31P{1H} NMR (121.4 MHz, C6D6): d
38.07. 11B{1H} NMR (128.3 MHz, C6D6): d ꢀ13.6.
IR: (CH2Cl2/KBr, cmꢀ1) mCN = 2162 (st). Anal. Calc.
for C39H67BCuNP2: C, 68.26; H, 9.84; N, 2.04. Found:
C, 68.01; H, 9.81; N, 2.24%.
2.2.12. [(3,5-Me2Ph)2B(CH2PtBu2)2]Cu(CO) (15)
(a) Solid 10 (11.3 mg, 17.5 lmol) was dissolved in
THF-d8 (0.7 mL) and placed in a J. Young NMR tube.
The tube was partially evacuated. CO gas (approximately
1 atm) was introduced to the J. Young tube, and the tube
was sealed. The solution was analyzed by NMR spectros-
copy. 1H NMR (300 MHz, THF-d8): d 7.00 (s, 4H, ortho-
(Me2C6H3)2B), 6.36 (s, 2H, para-(Me2C6H3)2B), 2.12 (s,
12H, ((CH3)2C6H3)2B), 2.03 (s, 3H, CH3CN), 1.53 (br,
4H, B(CH2PtBu)2), 1.14 (d, 18H, P(C(CH3)3)2,
substituted
phosphine
ligand
[(3,5-Me2Ph)2
B(CH2PtBu2)2]ꢀ (3). For example, reacting 1[ASN] with
CuI in THF/EtOH solution resulted in the near quantita-
tive generation of [[(p-tBuPh)2B(CH2PPh2)2]CuI][ASN]
(4), which could be isolated in high yield (Eq. (1)). Reac-
tions using the [Ph2B(CH2PPh2)2][ASN] ligand [8] pro-
vided similar results with CuI and CuCl; however, the
presence of tert-butyl substituents in the backbone of
the ligand framework increases the hydrocarbon solubil-
ity of these complexes.
3
3JP–H = 6.3 Hz), 1.12 (d, 18H, P(C(CH3)3)2, JP–H = 6.3
Hz). 13C{1H} NMR (125.7 MHz, THF-d8):
d
1
186.21(CO), 165.82 (br q, JB–C = 48 Hz), 134.66,
131.48, 124.55, 118.78 (CH3CN), 34.70 (d, P(C(CH3)3)2,
1
1JP–C = 7.2 Hz), 34.64 (d, P(C(CH3)3)2, JP–C = 7.2 Hz),
30.72 (br, P(C(CH3)3)2), 22.28 (((CH3)2C6H3)2B), 12.76
1
(br q, B(CH2PtBu)2, JB–C = 42 Hz), 1.01 (CH3CN).
ð1Þ

Table 1
X-ray diffraction experimental details for 6, 8 Æ THF Æ pentane, 9, 10 Æ 0.56THF Æ 0.22pentane, and 11
Compound
6
8 Æ THF Æ pentane
9
10 Æ 0.56THF Æ 0.22pentane
11
CCDC ID
238116
C26H49BClCuP2
533.39
238119
238120
C28H45BCuNP2
531.94
238118
C36H61BCuNP2 Æ 0.56(C4O) Æ 0.22(C5)
644.18 Æ 49.76
colorless block
0.26 · 0.26 · 0.19
monoclinic
238117
C42H69BCuP3
741.23
Empirical formula
Formula weight
Crystal description
Crystal size (mm)
Crystal system
Space group
C68H116B2BrCu2P4Tl Æ C5 Æ C4O
1490.54 Æ 124.02
colorless rod
yellow block
0.19 · 0.19 · 0.19
orthorhombic
P212121
colorless block
0.25 · 0.21 · 0.19
monoclinic
P21/n
colorless block
0.34 · 0.27 · 0.21
triclinic
0.33 · 0.18 · 0.13
monoclinic
P21/c
ꢀ
P21/n
P1
Unit cell dimensions
˚
a (A)
˚
7.3748(8)
11.7329(13)
33.404(4)
90
12.3182(11)
24.799(2)
27.773(3)
90
13.4206(9)
15.8317(11)
14.1571(9)
90
9.9223(8)
21.5707(18)
19.7938(17)
90
12.6936(12)
16.8198(16)
20.773(2)
104.598(2)
92.772(2)
90.192(2)
4286.3(7)
4
b (A)
˚
c (A)
a (ꢁ)
b (ꢁ)
c (ꢁ)
90
90
95.881(2)
90
98.3490(10)
90
100.6480(10)
90
3
˚
V (A )
2890.4(6)
4
1.226
8439.5(13)
4
1.271
2976.1(3)
4
1.187
4163.5(6)
4
1.107
Z
Dcalc(g cmꢀ3
)
1.149
0.648
l (mmꢀ1
T (K)
)
0.971
98
2.991
98
0.857
98
0.628
98
98
0.71073
26776
˚
Radiation k (A)
0.71073
17622
6558/295
0.0565, 0.1037
1.386
0.71073
127436
20450/775
0.0723, 0.1467
2.302
0.71073
17391
0.71073
72447
Reflections collected
Unique data/parameters
R1, wR2 (I > 2r(I))
Goodness-of-fit
6028/307
0.0349, 0.0738
1.401
9928/418
0.0530, 0.1100
2.087
18540/883
0.0469, 0.0753
1.240
ꢀ3
˚
Largest difference peak and hole (e A
)
0.987 and ꢀ0.825
2.510 and ꢀ1.144
0.676 and ꢀ0.295
0.867 and ꢀ0.449
0.808 and ꢀ0.559
P
P
P
P
R1 = iFoj ꢀ jFci/ jFoj, wR2 = { [w(Fo ꢀ Fc2)2]/ [w(Fo2)2]}1/2
.
2

J. Christopher Thomas, J.C. Peters / Polyhedron 23 (2004) 2901–2913
2907
Similar attempts to prepare 1:1 adducts of copper(I)
halides using the alkyl substituted phosphine ligands
2[Li] or 3[Li] gave more complicated results. For exam-
ple, the reaction of copper(I) iodide with either 2[Li] or
3[Li] resulted in the immediate precipitation of black
sediment with concomitant phosphine degradation,
ascertained by 31P{1H} and 11B{1H} NMR spectroscop-
ies. By contrast, combining copper(I) chloride and 3[Li]
in THF solution provided one major product (31P{1H}
NMR). Spectroscopic and elemental analysis proved
The spectroscopic identification of 6 was supported
by the independent synthesis of a structurally analogous
species, {PhB(CH2PtBu2)2}CuCl (7). The reaction be-
tween the neutral borane PhB(CH2PtBu2)2 and CuCl
in THF solution provided a high yield route to 7 (97%
yield) 1. The phosphine precursor PhB(CH2PtBu2)2
was readily generated by the addition of two equiv of
LiCH2PtBu2 to PhBCl2 in diethyl ether. Neutral 7 has
two important spectroscopic features. First, its
11B{1H} NMR spectrum (singlet at 75.2 ppm) confirms
the three-coordinate nature of the boron atom [16]. Sec-
ond, the 31P{1H} NMR chemical shift of 7 (23.11 ppm)
is consistent with the resonance ascribed to 6 (23.75
ppm).
To circumvent ligand degradation pathways, alterna-
tive copper(I) sources and the use of thallium phosphine
reagents were examined. Upon addition of a THF solu-
tion of 3[Tl] to Me2S Æ CuBr, thallium bromide precipi-
tated from solution. NMR analysis of the reaction
solution showed one major product. XRD analysis of
crystals obtained from the reaction solution provided
consistent
with
the
formation
of
[[(3,5-
Me2Ph)2B(CH2PtBu2)2]CuCl][Li(THF)4] (5) (Eq. (2)).
The clean preparation of copper(I) halides using the al-
kyl substituted phosphine ligands 2 and 3 appears to re-
quire a less redox susceptible copper(I) synthon (i.e.,
CuCl instead of CuI).
the
unexpected
molecular
structure,
[{[(3,5-
Me2Ph)2B(CH2PtBu2)2]Cu}2(l-Br)]Tl (8), shown in
Fig. 3. As is evident, only one-half of an equivalent of
TlBr is lost in the reaction (Eq. (3)).
ð2Þ
A significant body of work on {P2CuX} complexes
(P = phosphine, X = Cl, Br, I) shows that their coordi-
nation geometry can vary between three-coordinate
(P2CuX) or four-coordinate with bridging halides
({P2Cu(l-X)}2) [12,13]. For some phosphines, such as
PPh3, structural data have been obtained for both forms
[12b,12c]. A related example containing the tert-butyl
substituted chelating bis(phosphine) ligand dtbpe
(dtbpe = tBu2PCH2CH2PtBu2) provided the dimeric
structure {(dtbpe)Cu(l-Cl)}2 [14]. It is therefore possible
that 4 and 5 exist as either three-coordinate monomers,
or four-coordinate, bridged dimers in solution. An equi-
librium mixture of the two conformations may also pre-
vail in solution.
The reaction between 3[Li] and several copper(I) ha-
lide reagents provides a common secondary product.
For instance, the reaction between 3[Li] and CuCl pro-
vided a mixture of three phosphine containing products
(31P{1H} NMR). Along with the formation of the dom-
inant product 5 (>80%), two minor products were ob-
served. One of the minor products proved to be
isolable by fractional crystallization, and XRD analysis
of crystals thus obtained established its identity as {(3,5-
Me2Ph)B(CH2PtBu2)2}CuCl (6) (Fig. 2). Neutral 6 re-
sults from the loss of an aryl ring from the borate ligand,
generating a neutral bis(phosphino)borane ligated to
copper(I) chloride. Potentially related examples of
(phosphino)borate ligand degradation have been
observed previously [15]. In all of these cases, a bor-
on–carbon bond is cleaved at the boron–methylene link.
The present example demonstrates that the boron–aryl
link is also susceptible to cleavage.
ð3Þ
The structure of 8 shows two copper centers con-
nected by a linear bromide bridge, thus providing a
monoanionic dinuclear copper species with one thallium
counter-cation. A common plane cuts through each of
the phosphine, copper, bromide, and boron atoms of
8. The chelate phosphine ligand exists in its typical
twisted boat conformation [8,17]. In the molecular struc-
ture, the thallium atom resides in the pocket formed by
the two aryl rings of the borate anion. This thallium
coordination environment is similar to that observed
in the molecular structure of [Ph2B(CH2PPh2)2]Tl
(3[Tl]) [8]. Halide-bridged systems are well known for
copper(I), although there are few structurally character-
ized examples of copper centers bridged by a single ha-
lide [18]. This example appears to be structurally unique
amongst phosphine-coordinated copper(I) species. In
addition, all previous structurally characterized exhibit
a copper–halide–copper angle that is significantly bent.
The present example contains a linear halide bridge
(Cu1–Br–Cu2 = 178.00(6)ꢁ). Attempts to induce loss of
TlBr in solution by the addition of a donor ligand to
8, such as PMe3, pyridine, or acetonitrile, have not been
successful.

2908
J. Christopher Thomas, J.C. Peters / Polyhedron 23 (2004) 2901–2913
Fig. 3. Displacement ellipsoid representation (50%) of [{[(3,5-Me2Ph)2B(CH2PtBu2)2]Cu}2(l-Br)]Tl Æ THF Æ pentane (8 Æ THF Æ pentane). Hydrogen
˚
atoms and solvent molecules are omitted for clarity. Selected interatomic distances (A) and angles (ꢁ): P1–Cu1, 2.238(2); P2–Cu1, 2.230(2); P3–Cu2,
2.235(2); P4–Cu2, 2.231(2); Cu1–Br, 2.3660(12); Cu2–Br, 2.3638(12); B1–Cu1, 3.819(8); B2–Cu2, 3.829(8) and P1–Cu1–P2, 110.67(7); P1–Cu1–Br,
125.55(7); P2–Cu1–Br, 123.78(7); P3–Cu2–P4, 110.60(7); P3–Cu2–Br, 124.63(7); P4–Cu2–Br, 124.70(7); Cu1–Br–Cu2, 178.00(6).
3.2. Neutral three-coordinate acetonitrile copper(I)
complexes
An X-ray diffraction study verified the three-
coordinate nature of 9 (Fig. 4). The bis(phosphino)bor-
ate ligand is again in a twisted boat conformation. Two
parameters of further note from the molecular structure
of 9 are the B–Cu distance and the nature of the coordi-
nated acetonitrile ligand. In other structures of transi-
tion metal complexes coordinated by bis(phosphino)
borate ligands, the B–Cu distance in the twisted-
boat conformation has typically been observed at
To access more substitutionally labile copper(I) com-
plexes, the copper(I) reagent [Cu(CH3CN)4][PF6] proved
effective. Reaction of the alkyl-substituted phosphine
ligands 2[Li] or 3[Li] with [Cu(CH3CN)4][PF6] in THF
solution led to rapid formation of the three-coordinate
products [Ph2B(CH2PiPr2)2]Cu(NCCH ) (9) and [(3,5-
3
Me2Ph)2B(CH2PtBu2)2]Cu(NCCH3) (10) (Eqs. (4) and
(5)). Isolated yields of pure 9 were low (ca. 40%) due
to the difficulty in separating [Li(solvent)x][PF6] from
9. In comparison, 10 was isolated in much higher yield
(80%). Both compounds have been thoroughly charac-
terized by NMR spectroscopy and elemental analysis.
The IR spectra for 9 and 10 show mCN bands at 2265
and 2267 cmꢀ1, respectively. These stretches are consist-
ent with acetonitrile acting as a weakly bound r-donor.
Previously reported IR data for phosphine-coordinated
copper(I) acetonitrile complexes show a wide range of
C„N stretching frequencies (2268–2361 cmꢀ1), all of
which are above the value for the free ligand (CH3CN,
thin film on KBr: 2253 cmꢀ1) [19].
B–M = 3.91–4.12 A (M = Fe, Co, Rh, Pd, Pt). In the
structure of 9 and the other three-coordinate structures
presented in the present study, the B–M distance is rel-
˚
˚
atively short (9: B–Cu = 3.823(2) A). This is due to an
ð4Þ
ð5Þ
Fig.
4. Displacement
ellipsoid
representation
(50%)
of
[Ph2B(CH2PiPr2)2]Cu(NCCH3) (9). Hydrogen atoms are omitted for
˚
clarity. Selected interatomic distances (A) and angles (ꢁ): P1–Cu,
2.2349(6); P2–Cu, 2.2556(6); Cu–N, 1.934(2); B–Cu, 3.823(2) and P1–
Cu–P2, 103.35(2); P1–Cu–N, 133.25(5); P2–Cu–N, 118.98(5).

J. Christopher Thomas, J.C. Peters / Polyhedron 23 (2004) 2901–2913
2909
coordinate donor adduct complexes. Accordingly,
replacement of the labile acetonitrile complex 10 is af-
fected by a variety of donor ligands (Eq. (6)). Reaction
of 10 with dimethylphenylphosphine (PMe2Ph), trimeth-
ylphosphine sulfide (S@PMe3), 2,6-lutidine, and tert-
butylisonitrile (tBuNC) in THF solution provides the
corresponding complexes [(3,5-Me2Ph)2B(CH2PtBu2)2]-
Cu(PMe2Ph)
(11),
[(3,5-Me2Ph)2B(CH2PtBu2)2]-
Cu(S@PMe3) (12), [(3,5-Me2Ph)2B(CH2PtBu2)2]Cu(2,6-
lutidine) (13), and [(3,5-Me2Ph)2B(CH2PtBu2)2]Cu(CNt-
Bu) (14). All of these products can be isolated in high
yield (85–95%) and the reactions are complete in less
than 15 min at ambient temperature. In addition to
PMe2Ph, several other phosphine donors were also
examined. Triethylphosphine provided a well-defined
three-coordinate adduct complex, whereas PMePh2 pro-
vided a mixture of the expected three-coordinate adduct
complex and also a second, unidentified diamagnetic
product. PPh3 does not substitute the acetonitrile ligand
of 10, presumably due to steric congestion. Addition of
the phosphite ligand P(OPh)3 gradually consumes 10,
but results in overall complex degradation to ill-defined
products. Substitution reactions of 10 by simple olefins
was also surveyed. No reaction was observed (1H and
31P{1H} NMR) between 10 and the potentially g2-do-
nors ethylene, 1-hexene, styrene, and azobenzene (1–10
equiv) in THF solution. This lack of reactivity is consist-
ent with previous literature studies that suggest that cop-
per(I) complexes supported by phosphine ligands do not
form stable olefin adducts readily. Those that have been
observed have typically required the presence of a large
excess of the olefin [21] or chelation effects [22] to pro-
vide a Cu-olefin adduct species.
Fig. 5. Displacement ellipsoid representation (50%) of [(3,5-
Me2Ph)2B(CH2PtBu2)2]Cu(NCCH3) Æ 0.56THF Æ 0.22pentane (10 Æ 0.56
THF Æ 0.22pentane). Hydrogen atoms and solvent molecules are
omitted for clarity. Selected interatomic distances (A) and angles (ꢁ):
P1–Cu, 2.2421(8); P2–Cu, 2.2333(8); Cu–N, 1.930(2); B–Cu, 3.861(3)
and P1–Cu–P2, 108.55(3); P1–Cu–N, 124.94(7); P2–Cu–N, 126.49(7).
˚
expansion of the P–M–P angle (103.35(2)ꢁ) that results
from the three-coordinate structure and the sterically
small acetonitrile ligand. The acetonitrile ligand of 9
adopts a distorted coordination mode. Rather than
bisecting the P–Cu–P linkage, the nitrile is canted below
the plane of these three atoms, favoring one side of the
C2 axis. This is likely a solid-state phenomenon: the
solution spectra of 9 are consistent with a molecule that
contains a C2 axis.
An X-ray diffraction study carried out on 10 also
shows a trigonal planar three-coordinate copper center
(Fig. 5). The structural parameters of 10 are quite similar
to those found for 9, with two minor differences. First,
the acetonitrile ligand is coincident with the C2 axis of
the molecule and thus colinear with the B–Cu vector.
Second, the P–Cu–P angle is modestly wider
(108.55(3)ꢁ) than that observed in 9 (103.35(2)ꢁ). The
slightly wider bite angle of the bis(phosphine) does not
result in a corresponding contraction of the B–Cu dis-
tance; instead, a slight increase in the B–Cu distance of
ð6Þ
The tris(phosphine) complex 11 was structurally
characterized by X-ray diffraction, verifying its three-
coordinate geometry (Fig. 6). The structural parameters
of 11 reflect the incorporation of a more sterically
demanding phosphine donor ligand relative to the aceto-
nitrile ligand of 10. For example, the P–Cu–P angle is re-
duced (103.87(3)ꢁ in 11 versus 108.55(3)ꢁ in 10) and the
˚
10 as compared to 9 (3.861(3) vs. 3.823(2) A) is observed.
The acetonitrile compounds 9 and 10 are structurally dis-
tinctive examples of monomeric, phosphine-supported
nitrile adducts of 3-coordinate copper(I). A few related
examples of phosphine-coordinated copper nitrile com-
plexes have been structurally characterized previously
[20]. These examples are each either four-coordinate, or
contain multiple metal centers (e.g., Cu2 or RhCu).
˚
B–Cu distance is increased (3.972(3) Ain 11 versus
˚
3.861(3) A in 10). Also, the average P–Cu bond lengths
for the bis(phosphino)borate ligand are modestly longer
˚
˚
3.3. Substitution chemistry of the sterically encumbered
complex 10
(2.27 A in 11 versus 2.24 A in 10), likely reflecting the
greater electron-releasing nature of PMe2Ph as com-
pared to acetonitrile.
The well-defined three-coordinate acetonitrile com-
plexes 9 and 10 serve as useful precursors to other three
Neutral 11 is similar to previous structurally charac-
terized P3Cu complexes (P = trialkyl phosphine). Several

2910
J. Christopher Thomas, J.C. Peters / Polyhedron 23 (2004) 2901–2913
[H2B(3,5-(CF3)2Pz)2]Cu(2,4,6-collidine). Similar to 13,
the monoanionic borate-based [H2B(3,5-(CF3)2Pz)2]ꢀ
provides a neutral, three-coordinate copper(I) center.
The isonitrile complex [(3,5-Me2Ph)2B(CH2PtBu2)2]-
Cu(CNtBu) (14) is structurally distinct in that it repre-
sents what is to our knowledge the only example of a
phosphine-supported, three-coordinate monoisonitrile
complex of copper(I). Four-coordinate copper(I) com-
plexes featuring terminal isocyanide ligands more typi-
cally feature either three phosphine ligands and one
isonitrile ligand, or two phosphines and two isocyanide
ligands [33–37]. A key spectroscopic feature of metal-
bound isocyanides is their infrared signature. The infra-
red spectrum of 14 shows a mCN band at 2162 cmꢀ1. This
value is presented in Table 2 along with several other
previously reported copper(I) complexes containing a
single tert-butyl isonitrile ligand [38–43]. As can be seen,
most of the examples have mCN values greater than that
observed for free CNtBu. This increase in the C„N
stretching frequency has been attributed to both poor
back-donation from the copper d-orbitals into the lig-
and p* orbitals, and to a strong r-donor effect that
polarizes the C„N bond [44,45]. Thus, the isonitrile lig-
and in 14 can be considered as primarily a strong r-
donor in this context.
Fig. 6. Displacement ellipsoid representation (50%) of [(3,5-
Me2Ph)2B(CH2PtBu2)2]Cu(PMe2Ph) (11). Second molecule in the
asymmetric unit and hydrogen atoms are omitted for clarity. Selected
˚
interatomic distances (A) and angles (ꢁ): P1–Cu1, 2.2714(8); P2–Cu1,
2.2707(8); Cu1–P3, 2.2477(8); B1–Cu1, 3.972(3) and P1–Cu1–P2,
103.87(3); P1–Cu1–P3, 127.29(3); P2–Cu1–P3, 128.84(3).
structures reported for [(Ph3P)3Cu]+ [23] and the related
[{(p-MeOPh)3P}3Cu]+ cation [24] have shown a mean
˚
Cu–P length of 2.295 A and P–Cu–P angles near 120ꢁ.
Also, Mathey and coworkers reported a macrocyclic
P3-phosphinine ligand system in which a copper center
lies in a distorted trigonal planar coordination geometry
[25]. Additionally, there are two reports of bimetallic
[Cu2(g1:g1-L2)3]2+ (L2 = dmpm, (Ph2P)2py), where the
copper centers are both in highly symmetric trigonal pla-
nar environments [26]. The structures of these homolep-
tic phosphine adducts are relatively C3 symmetric,
whereas the structure of 11 is better described as C2v
due to the geometric constraint imposed by the chelated
bis(phosphine) ligand. A similarly distorted structure
has been reported for dicationic [{(dppf)Cu}2(g1:g1-
dppf)]2+ [27], which has Cu–P bond lengths of 2.280
We also surveyed the generation of a monocarbonyl
copper complex analogous to 14. To our knowledge,
there are as yet no examples of well-defined copper carbo-
nyl complexes supported by phosphine ligands. This is
consistent with the observations of related isonitrile com-
plexes, where copper(I) has been characterized as a rela-
tively poor p-donor. We have found that the reaction
between 10 and excess CO gas results in the formation
of an unstable carbonyl adduct species that can be formu-
lated as [(3,5-Me2Ph)2B(CH2PtBu2)2]Cu(CO) (15). In
THF solution, excess carbon monoxide appears to dis-
place the acetonitrile ligand, resulting in a shift in the
31P{1H} NMR resonance from 36.4 to 42.3 ppm. If CO
is removed under vacuum, the acetonitrile adduct is
˚
˚
˚
A, 2.283 A, and 2.260 A and P–Cu–P angles of 124.6ꢁ,
123.4ꢁ, and 111.3ꢁ.
Table 2
Infrared resonances (mCN
complexes
A complex related to 11 is the phosphine sulfide ad-
duct [(3,5-Me2Ph)2B(CH2PtBu2)2]Cu(S@PMe3) (12). A
structurally related species has been reported:
[{(dppf)Cu}2(g1:g1-dppfS2)][BF4]2 [28]. Complex 12
exhibits remarkably poor solubility (<5 mg/mL) in ben-
zene and THF solution, distinct from 11, 13, and 14.
Similar to 12, the lutidine derivative [(3,5-
Me2Ph)2B(CH2PtBu2)2]Cu(2,6-lutidine) (13) contains
an uncommon coordination environment for copper(I).
The sterically hindered pyridines 2,6-lutidine and 2,4,6-
collidine have been used previously to prepare two- and
three-coordinate copper complexes [29–32]. In almost
all of these cases, the complexes are homoleptic pyridine
cations, or include a single halide or pseudo-halide donor
[29–31]. One notable exception reported by Omary et al.
[32] is the fluorinated bis(pyrazolyl)borate derivative,
) for some copper(I) monoisonitrile
Complex
mCN (cmꢀ1
)
Ref.
[HB{3,5-(CF3)2pz}3]Cu(CNtBu)
[(Ph3P)3Cu(CNEt)][BF4]
CpCu(CNtBu)
2196a
2193b
2170a
2162c
2155d
2148a
2140d
2138e
2102b
[38]
[37]
[39]
[(3,5-Me2Ph)2B(CH2PtBu2)2]Cu(CNtBu) (14)
[HB(Pz)3]Cu(CNtBu)
[40]
[41]
[42]
[19]
[43]
[CpCo{P(OMe)2O}3]Cu(CNtBu)
[j3-B(Pz)4]Cu(CNtBu)
tBuNC
(tBuO)Cu(CNtBu)
a
KBr.
Nujol.
b
c
THF/KBr.
Not reported.
Neat.
d
e

J. Christopher Thomas, J.C. Peters / Polyhedron 23 (2004) 2901–2913
2911
regenerated as indicated by the return of the 36.4 ppm res-
onance. Infrared analysis of green solids isolated by dry-
ing a sample of 10 under a stream of CO gas revealed a
single infrared band at 2084 cmꢀ1, consistent with a
metal-bound monocarbonyl species. The carbonyl species
15 is not stable in the absence of excess CO, apparently
decaying to solvent-bound species with concomitant loss
of CO. For instance, if a THF solution of 10 is dried un-
der a stream of CO gas, the resulting pale green solids that
are isolated display a 31P{1H} NMR resonance at 44 ppm
upon dissolution in benzene-d6. This resonance gradually
disappears unless a blanket of CO is preserved above the
NMR sample solution. A single new resonance grows in
at 38 ppm, which may be indicative of a benzene solvent
adduct of Cu(I). The lability of the putative monocarbo-
nyl species is consistent with previous observations for
phosphine-supported copper [20n].
provided assistance with X-ray crystallography. Chris-
tine Thomas generously provided
a
sample of
PhB(CH2PtBu2)2. J.C.T. is grateful to the NSF and to
the Moore Foundation for graduate research
fellowships.
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