Pincer-like amido complexes of platinum, palladium, and nickel

Article abstract of DOI:10.1021/ic010336p

The ligands bis(8-quinolinyl)amine (BQAH, 1), (2-pyridin-2-yl-ethyl)-(8-quinolinyl)amine (2-pyridin-2-yl-ethyl-QAH, 2), o-dimethylaminophenyl(8-quinolinyl)amine (o-(NMe2)Ph-QAH, 3), and 3,5-dimethylphenyl(8-quinolinyl)-amine (3,5-Me₂Ph-QAH, 4) have been prepared in high yield from aryl halide and amine precursors by palladium-catalyzed coupling reactions. Deprotonation of 1 with ⁿBuLi in toluene affords the lithium amide complex [Li] [BQA] (5), whose dimeric solid-state crystal structure is presented. Lithium amide 5 was transmetalated.by TIOTf to afford the thallium(1) amido complex [T1][BQA] (6). An X-ray structural study of 6 shows it to be a 1:1 complex of the BQA ligand and T1. Entry into the group 10 chemistry of the parent ligand 1 was effected by both protolytic and metathetical strategies. Thus, the divalent chloride complexes (BQA)PtCl (7), (BQA)PdCl (8), and (BQA)-NiCl (9) were prepared and fully characterized. An X-ray structural study for each of these three complexes shows them to be well-defined, square-planar complexes in which the auxiliary BQA ligand binds in a planar, η³-fashion. For comparison, the reactivity of ligands 2-4 with (COD)PtCl₂ was studied. While reaction with ligand 2 afforded an ill-defined product mixture, ligands 3 and 4 reacted with (COD)PtCl₂ to generate the unusual alkyl complexes (o-(NMe₂)Ph-QA)Pt(1,2-η²-6-σ-cycloocta- 1,4-dienyl) (10) and (3,5-Me₂Ph-QA)Pt(1,2-η²-6-σ-cycloocta- 1,4-dienyl) (11), both of which have been structurally characterized.

Full text of DOI:10.1021/ic010336p

Inorg. Chem. 2001, 40, 5083-5091
Pincer-like Amido Complexes of Platinum, Palladium, and Nickel
Jonas C. Peters,* Seth B. Harkins, Steven D. Brown, and Michael W. Day
5083
Division of Chemistry and Chemical Engineering, Arnold and Mabel Beckman Laboratories of Chemical
Synthesis, California Institute of Technology, Pasadena, California 91125
ReceiVed March 27, 2001
The ligands bis(8-quinolinyl)amine (BQAH, 1), (2-pyridin-2-yl-ethyl)-(8-quinolinyl)amine (2-pyridin-2-yl-ethyl-
QAH, 2), o-dimethylaminophenyl(8-quinolinyl)amine (o-(NMe2)Ph-QAH, 3), and 3,5-dimethylphenyl(8-quinolinyl)-
amine (3,5-Me2Ph-QAH, 4) have been prepared in high yield from aryl halide and amine precursors by palladium-
catalyzed coupling reactions. Deprotonation of 1 with nBuLi in toluene affords the lithium amide complex [Li][BQA]
(5), whose dimeric solid-state crystal structure is presented. Lithium amide 5 was transmetalated by TlOTf to
afford the thallium(I) amido complex [Tl][BQA] (6). An X-ray structural study of 6 shows it to be a 1:1 complex
of the BQA ligand and Tl. Entry into the group 10 chemistry of the parent ligand 1 was effected by both protolytic
and metathetical strategies. Thus, the divalent chloride complexes (BQA)PtCl (7), (BQA)PdCl (8), and (BQA)-
NiCl (9) were prepared and fully characterized. An X-ray structural study for each of these three complexes
shows them to be well-defined, square-planar complexes in which the auxiliary BQA ligand binds in a planar,
η3-fashion. For comparison, the reactivity of ligands 2-4 with (COD)PtCl2 was studied. While reaction with
ligand 2 afforded an ill-defined product mixture, ligands 3 and 4 reacted with (COD)PtCl2 to generate the unusual
alkyl complexes (o-(NMe2)Ph-QA)Pt(1,2-η2-6-σ-cycloocta-1,4-dienyl) (10) and (3,5-Me2Ph-QA)Pt(1,2-η2-6-σ-
cycloocta-1,4-dienyl) (11), both of which have been structurally characterized.
I. Introduction
enables the generation of a readily prepared family of useful,
monoanionic amido ligands. Notably, although hard amido
The study of late transition elements has gained increasing
momentum in recent years because of their potential for
catalyzing desirable transformations.1-4 A key feature of later
metals is that they tend to be both more tolerant to functional
groups and more robust toward air and moisture than their earlier
transition metal counterparts.5,6 In part because of these desirable
properties, industrially important late metal polymerization
catalysts are now under intense scrutiny.7 Furthermore, late
metal systems are being studied for their ability to couple the
activation and oxidation of light hydrocarbon substrates.8
To build new molecular systems relevant to these and related
goals, our group is pursuing complexes supported by robust,
anionic chelating ligands.9 This manuscript serves two primary
purposes. First, it presents a strategy for the synthesis of amido
ligands based upon an N-(8-quinolinyl) motif. This strategy
ligands can lead to undesirable reduction and/or degradation of
late metal complexes, the use of chelating amido ligands can
circumvent such problems.10 Second, this manuscript examines
the preparative and structural chemistries of the parent BQA
ligand, 1,11 with respect to both its synthetically useful lithium
and thallium reagents and, more importantly, its ability to
coordinate group 10 metal centers in a well-defined, tridentate
fashion. Our desire to explore the divalent group 10 chemistry
(8) For relevant papers to alkane activation at cationic mid to late metals,
see the following: (a) Stahl, S. S.; Labinger, J. A.; Bercaw, J. E.
Angew. Chem., Int. Ed. 1998, 37, 2181. (b) Arndtsen, B. A.; Bergman,
R. G.; Mobley, T. A.; Peterson, T. H. Acc. Chem. Res. 1995, 28, 154.
(c) Holtcamp, M. W.; Henling, L. M.; Day, M. W.; Labinger, J. A.;
Bercaw, J. E. Inorg. Chim. Acta 1998, 270, 467. (d) Shen, C. Y.;
Garcia-Zayas, E. A.; Sen, A. J. Am. Chem. Soc. 2000, 122, 4029. (e)
Sen, A. Acc. Chem. Res. 1998, 31, 550. (f) Tellers, D. M.; Bergman,
R. G. J. Am. Chem. Soc. 2000, 122, 954. (g) Periana, R. A.; Taube,
D. J.; Gamble, S.; Taube, H.; Satoh, T.; Fujii, H. Science 1998, 280,
560.
* To whom correspondence should be addressed. Fax: (626) 577-4088.
Tel: (626) 395-4036. E-mail: jpeters@caltech.edu.
(1) Abel, E. W., Stone, F. G. A., Wilkinson, G., Eds. ComprehensiVe
Organometallic Chemistry; Elsevier Science, Ltd.: Tarrytown, NY,
1995; Vols. 8-10.
(9) (a) Qian, B. X.; Henling, L. M.; Peters, J. C. Organometallics 2000,
19, 2805. (b) Thomas, J. C.; Peters, J. C. J. Am. Chem. Soc. 2001,
123, 5100. (c) Shapiro, I. R.; Jenkins, D. M.; Thomas, J. C.; Day, M.
W.; Peters, J. C. Chem. Commun., in press.
(2) Hegedus, L. S. Transition Metals in the Synthesis of Complex Organic
Molecules; University Science Books: Mill Valley, CA, 1994.
(3) Doyle, M. P.; Forbes, D. C. Chem. ReV. 1998, 98, 911.
(4) Gossage, R. A.; VanDeKuil, L. A.; van Koten, G. Acc. Chem. Res.
1998, 31, 423.
(5) Grubbs, R. H.; Chang, S. Tetrahedron 1998, 54, 4413.
(6) Joo, F.; Katho, A. J. Mol. Catal. A: Chem. 1997, 116, 3.
(7) For recent references pertaining to olefin polymerization using cationic
mid and late transition metals, see: (a) Ittel, S. D.; Johnson, L. K.;
Brookhart, M. Chem. ReV. 2000, 100, 1169. (b) Killian, C. M.;
Johnson, L. K.; Brookhart, M. Organometallics 1997, 16, 2005. (c)
Younkin, T. R.; Conner, E. F.; Henderson, J. I.; Friedrich, S. K.;
Grubbs, R. H.; Bansleben, D. A. Science 2000, 287, 460. (d) Britovsek,
G. J. P.; Bruce, M.; Gibson, V. C.; Kimberley, B. S.; Maddox, P. J.;
Mastroianni, S.; McTavish, S. J.; Redshaw, C.; Solan, G. A.;
Stromberg, S.; White, A. J. P.; Williams, D. J. J. Am. Chem. Soc.
1999, 121, 8728.
(10) For some relevant lead references, see: (a) Fryzuk, M. D.; Macneil,
P. A.; Rettig, S. J.; Secco, A. S.; Trotter, J. Organometallics 1982, 1,
918. (b) Fryzuk, M. D.; Leznoff, D. B.; Thompson, R. C.; Rettig, S.
J. J. Am. Chem. Soc. 1998, 120, 10126. (c) Deacon, G. B.; Gatehouse,
B. M.; Grayson, I. L.; Nesbit, M. C. Polyhedron 1984, 3, 753. (d)
Buxton, D. P.; Deacon, G. B.; Gatehouse, B. M.; Grayson, I. L.;
Wright, P. J. Acta Crystallogr., Sect. C 1985, 41, 1049. (e) Dori, Z.;
Eisenberg, R.; Steifel, E. I.; Gray, H. B. J. Am. Chem. Soc. 1970, 92,
1506. (f) Kawamoto, T.; Nagasawa, I.; Kuma, H.; Kushi, Y. Inorg.
Chim. Acta 1997, 265, 163. (g) Endres, H.; Keller, J.; Poveda, A. Z.
Naturforsch., B 1977, 32, 131. (h) Sacco, A.; Vasapollo, G.; Nobile,
C. F.; Piergiovanni, A.; Pellinghelli, M. A.; Lanfranchi, M. J.
Organomet. Chem. 1988, 356, 397.
(11) (a) Jenson, K. A.; Nielson, P. H. Acta Chem. Scand. 1964, 18, 1. (b)
Puzas, J. P.; Nakon, R.; Pertersen, J. L. Inorg. Chem. 1986, 25, 3837.
10.1021/ic010336p CCC: $20.00 © 2001 American Chemical Society
Published on Web 08/24/2001

5084 Inorganic Chemistry, Vol. 40, No. 20, 2001
Peters et al.
1
compared favorably with that previously reported. H NMR (CDCl3,
300 MHz, 25 °C): δ 10.65 (s, 1H), 8.97 (dd, J ) 1.7, 2.2 Hz, 2H),
8.16 (dd, J ) 1.7, 8.3 Hz, 2H), 7.92 (d, J ) 6.5 Hz, 2H), 7.58-7.42
(m, 4H), 7.34 (d, J ) 7 Hz, 2H). 13C NMR (CDCl3, 75 MHz, 25 °C):
δ 148.1, 140.1, 138.8, 136.2, 129.1, 127.2, 121.7, 117.9, 110.1. LR-
MS (electrospray): calcd for C17H17N3 (M)+ m/z 271, found (M + H)+
m/z 272.
of 1 is motivated, in part, by the following rationale. Square-
planar, monoalkyl complexes of ligand 1 should adopt a
coordination geometry in which the alkyl group is forced to
occupy a coordination site trans to the amido nitrogen donor
group. Typically, divalent group 9 and 10 complexes containing
two strongly trans-effecting ligands adopt coordination geom-
etries that place these two ligands cis to one another.12 The BQA
ligand discriminates against such a cis preference, and our hope
is that resulting complexes will prove reactive at the site trans
to the amido nitrogen donor. In this regard, BQA-type ligands
are conceptually related to the popular family of anionic “pincer”
ligands, a class of ligands that now affords a rich reaction
chemistry among metals from groups 8, 9, and 10.13
II.B. Synthesis of 2-Pyridin-2-yl-ethyl-QAH, 2. A 200 mL reaction
vessel with a stir bar was charged with Pd2(dba)3 (0.170 g, 0.186 mmol),
rac-2,2′-bis(diphenylphosphino)-1,1′-binaphthyl (rac-BINAP) (0.232 g,
0.372 mmol), and toluene (20 mL) under a dinitrogen atmosphere. The
resulting solution was allowed to stir for 5 min, after which time
8-bromoquinoline (1.549 g, 7.45 mmol), 2-(2-aminoethyl)pyridine
(1.000 g, 8.19 mmol), and additional toluene (20 mL) were added. The
subsequent addition of NaOtBu (1.002 g, 10.43 mmol) caused the
reaction slurry to turn red, and the contents were stirred vigorously for
18 h at 90 °C. The final purple solution was cooled to ambient
temperature, and the solvent was removed in vacuo affording a viscous
violet liquid. Purification by flash chromatography on silica gel (1:1
toluene/ethyl acetate) yielded a red oil that was extracted with diethyl
ether, filtered, and dried under vacuum for 24 h to yield the desired
II. Experimental Section
All manipulations were carried out using standard Schlenk or
glovebox techniques under a dinitrogen atmosphere. Unless otherwise
noted, solvents were deoxygenated and dried by thorough sparging with
N2 gas followed by passage through an activated alumina column.
Nonhalogenated solvents were typically tested with a standard purple
solution of sodium benzophenone ketyl in tetrahydrofuran to confirm
effective oxygen and moisture removal. The reagent 8-bromoquinoline
was synthesized following a literature procedure.14 The preparations
of 2-bromo-N,N-dimethylaniline,15 (COD)PdCl2,16 (COD)PdMeCl,17
(DME)NiCl2,18 (COD)PtCl2,19 and (COD)PtMeCl16 were carried out
following literature procedures. Other reagents were purchased from
commercial vendors and used without further purification. Elemental
analyses were performed by Desert Analytics, Tucson, Az. A Varian
Mercury-300 NMR spectrometer or a Varian Inova-500 NMR spec-
trometer was used to record 1H and 13C NMR spectra unless otherwise
1
product (1.584 g, 85%). H NMR (CDCl3, 500 MHz, 25 °C): δ 8.60
(dd, J ) 4.2, 1.5 Hz, 1H), 8.51 (d, J ) 3.9 Hz, 1H), 7.94 (dd, J ) 8.1,
2.0 Hz, 1H), 7.49 (m, 1H), 7.30 (m, 1H), 7.25 (m, 1H), 7.0-7.12 (m,
2H), 6.95 (dd, J ) 8.1, 1.5 Hz, 1H), 6.66 (d, J ) 6.9 Hz, 1H), 6.31 (br
s, NH), 3.66 (m, 2H), 3.15 (t, J ) 7 Hz, 2H). 13C NMR (CDCl3, 75
MHz, 25 °C): δ 159.8, 149.7, 147.0, 144.8, 138.4, 136.6, 136.1, 128.9,
128.0, 123.6, 121.6, 121.5, 114.0, 104.9, 43.4, 37.9. GC-MS (EI):
calcd for C16H15N3 (M)+ m/z 249, found (M)+ m/z 249.
II.C. Synthesis of o-(NMe2)Ph-QAH, 3. A 200 mL reaction vessel
equipped with a Teflon stopcock and stir bar was charged with Pd2(dba)3
(0.915 g, 0.999 mmol), 1,1′-bis(diphenylphosphino)ferrocene (DPPF)
(1.11 g, 2.00 mmol), and toluene (100 mL) under a dinitrogen
atmosphere. The resulting solution was allowed to stir for 5 min, after
which time 8-aminoquinoline (3.60 g, 0.0250 mol), N,N-dimethyl-o-
bromoaniline (5.00 g, 0.025 mol), and NaOtBu (2.88 g, 0.030 mol)
were added. This solution was stirred vigorously for 3 days at 110 °C
after which time it was cooled to room temperature (rt) and filtered
through a silica plug. Ethyl acetate was used to elute the plug to ensure
complete removal of the desired product. Removal of volatiles in vacuo
yielded a crude red liquid. The remaining starting materials were
removed via vacuum distillation, and the resulting liquid was filtered
once more through a silica gel plug. The orange residue obtained after
drying in vacuo (3.56 g, 54%) solidified upon standing at rt for 5 days.
1H NMR (CDCl3, 300 MHz, 25 °C): δ 8.85 (dd, J ) 1.8, 4.2 Hz,
1 H), 8.71 (s, 1H), 8.13 (dd, J ) 1.5, 8.1 Hz, 1 H), 7.67 (dd, J ) 1.8,
8.1 Hz, 1H), 7.60 (dd, J ) 1.2, 7.8 Hz, 1H), 7.45 (dd, J ) 1.5, 6.0 Hz,
1H), 7.43 (m, 1H), 7.24-6.97 (m, 5H), 2.75 (s, 6H). 13C NMR
(CDCl3, 75 MHz, 25 °C): δ 147.6, 145.1, 140.0, 139.3, 136.1, 136.0,
129.1, 127.4, 123.2, 121.6, 119.4, 117.8, 116.4, 107.8, 44.1. LR-MS
(electrospray): calcd for C17H17N3 (M)+ m/z 263, found (M + H)+
m/z 264.
1
stated. H and 13C NMR chemical shifts were referenced to residual
solvent. MS data for samples were obtained by injection of an
acetonitrile solution into a Hewlett-Packard 1100MSD mass spectrom-
eter (ES+) or an Agilent 5973 mass selective detector (EI). Deuterated
chloroform and benzene were degassed and dried over activated 3 Å
molecular sieves prior to use.
II.A. Synthesis of BQAH, 1. A 200 mL reaction vessel equipped
with a Teflon stopcock and stir bar was charged with Pd2(dba)3 (0.176
g, 0.192 mmol), rac-2,2′-bis(diphenylphosphino)-1,1′-binaphthyl (rac-
BINAP) (0.239 g, 0.384 mmol), and toluene (30 mL) under a dinitrogen
atmosphere. The resulting solution was allowed to stir for 5 min, after
which time 8-bromoquinoline (2.00 g, 9.61 mmol), 8-aminoquinoline
(1.39 g, 9.64 mmol), and additional toluene (70 mL) were added. The
subsequent addition of NaOtBu (1.11 g, 11.5 mmol) resulted in a red
solution that was stirred vigorously for 3 days at 110 °C. The solution
was then allowed to cool and filtered through a silica plug that was
then extracted with dichloromethane to ensure complete removal of
the desired product. Concentration of the collected extracts and removal
of solvent yielded a crude red solid (2.37 g, 91%). Purification by flash
chromatography on silica gel (4:1 toluene/ethyl acetate) yielded orange,
solid bis(8-quinolinyl)amine (1.95 g, 75%) as a spectroscopically pure
and synthetically useful compound. Characterization data for 1
II.D. Synthesis of 3,5-Me2Ph-QAH, 4. A 200 mL reaction vessel
equipped with a Teflon stopcock and stir bar was charged with Pd2(dba)3
(0.222 g, 0.242 mmol), 1,1′-bis(diphenylphosphino)ferrocene (DPPF)
(0.268 g, 0.483 mmol), and 20 mL of toluene under a dinitrogen
atmosphere. The resulting solution was allowed to stir for 5 min, after
which time 8-aminoquinoline (0.873 g, 6.05 mmol), 3,5-dimethyl-
bromobenzene (1.12 g, 6.05 mmol), and NaOtBu (1.16 g, 12.1 mmol)
were added. The solution was allowed to stir at 110 °C for 24 h, after
which time it was allowed to cool and filtered over silica gel. Toluene
was then removed in vacuo, and flash chromatography on silica gel
(15:1 toluene/ethyl acetate) yielded spectroscopically pure 4 as an
(12) (a) Vila, J. M.; Pereira, M. T.; Ortigueira, J. M.; Lata, D.; Lopez Torres,
M.; Fernandez, J. J.; Fernandez, A.; Adams, H. J. Organomet. Chem.
1998, 566, 93. (b) Crespo, M.; Solans, X.; Font-Bardia, M. Polyhedron
1998, 17, 3927. (c) Gandelman, M.; Vigalok, A.; Shimon, L. J. W.;
Milstein, D. Organometallics 1997, 16, 3981.
(13) (a) Liu, F. C.; Pak, E. B.; Singh, B.; Jensen, C. M.; Goldman, A. S.
J. Am. Chem. Soc. 1999, 121, 4086. (b) Sundermann, A.; Uzan, O.;
Milstein, D.; Martin, J. M. L. J. Am. Chem. Soc. 2000, 122, 7095. (c)
Dani, P.; Karlen, T.; Gossage, R. A.; Gladiali, S.; van Koten, C. Angew.
Chem., Int. Ed. 2000, 39, 743.
(14) Butler, J. L.; Gordon, M. J. Heterocycl. Chem. 1975, 12, 1015.
(15) Kelly, D. P.; Bateman, S. A.; Hook, R. J.; Martin, R. F.; Reum, M.;
Rose, M.; Whittaker, A. R. D. Aust. J. Chem. 1994, 47, 1751.
(16) Chatt, L.; Vallarino, L. M. J. Chem. Soc. 1957, 3413.
(17) lke, R. E.; Ernsting, J. M.; Spek, A. L.; Elsevier, C. J.; van Leewen,
P. W. N. M.; Vrieze, K. Inorg. Chem. 1993, 32, 5769.
1
orange liquid (1.28 g, 85%). H NMR (CDCl3, 300 MHz, 25 °C): δ
8.79 (dd, J ) 1.5, 4.2 Hz, 1H), 8.21 (s, 1H), 8.12 (dd, J ) 1.8, 8.4 Hz,
1H), 7.52-7.20 (m, 4H), 7.05 (s, 2H), 6.72 (s, 1H), 2.40 (s, 6H). 13C
NMR (CDCl3, 75 MHz, 25 °C): δ 147.3, 141.8, 140.5, 139.1, 138.3,
136.3, 129.0, 128.5, 124.1, 121.7, 118.0, 116.3, 108.0, 21.8. LR-MS
(electrospray): calcd for C17H16N2 (M+) m/z 248, found (M + H)+
m/z 249.
(18) Ward, L. G. L. Inorg. Synth. 1971, 13, 154.
(19) Clark, H. C.; Manzer, L. E. J. Organomet. Chem. 1973, 59, 411.

Amido Complexes of Pt, Pd, and Ni
Inorganic Chemistry, Vol. 40, No. 20, 2001 5085
II.E. Synthesis of [Li][BQA], 5. A solution of 1.6 M n-butyllithium
in hexanes (4.82 mL, 7.71 mmol) diluted with toluene (20 mL) was
added dropwise over 30 min to a stirring solution of BQAH (2.089 g,
7.71 mmol) in toluene (250 mL) at -78 °C. The reaction mixture was
then allowed to warm slowly to ambient temperature. After the reaction
mixture was stirred for an additional 24 h, the solvent was removed in
vacuo, affording a bright orange solid. The product was lyophilized
from 50 mL of benzene, washed with petroleum ether (3 × 30 mL),
and dried in vacuo affording spectroscopically pure 5 (1.880 g, 88%).
1H NMR (CDCl3, 300 MHz, 25 °C): δ 7.84 (d, J ) 7.7 Hz, 2H), 7.70
(d, J ) 8.2 Hz, 2H), 7.54 (d, J ) 4.5 Hz, 2H), 7.31 (m, 2H), 6.81 (d,
J ) 7.7 Hz, 2H), 6.69 (m, 2H). 13C NMR (CDCl3, 126 MHz, 25 °C):
δ 156.0, 145.3, 145.2, 136.3, 130.3, 128.3, 120.0, 113.6, 112.4. Anal.
Calcd for C18H12N3Li: C, 77.98; H, 4.36; N, 15.16. Found: C, 77.92;
H, 4.41; N, 14.39.
petroleum ether (3 × 15 mL) and dried to afford spectroscopically pure
product 8 (915 mg, 62%). An analytically pure sample was obtained
from a hexanes/chloroform diffusion chamber. H NMR (CDCl3, 300
1
MHz, 25 °C): δ 8.95 (d, J ) 5 Hz, 2H), 8.20 (d, J ) 8.2 Hz, 2H),
7.65 (d, J ) 8.2 Hz, 2H), 7.46 (m, 2H), 7.37 (m, 2H), 7.07 (d, J ) 8.2
Hz, 2H). 13C NMR (CDCl3, 75 MHz, 25 °C): δ 149.5, 148.9, 148.3,
138.8, 131.2, 129.5, 121.3, 115.1, 112.6. LR-MS (electrospray): calcd
for C18H12ClN3Pd (M)+ m/z 411, found (M - Cl)+ m/z 376. Anal. Calcd
for C18H12N3PdCl: C, 52.45; H, 2.93; N, 10.19. Found: C, 52.17; H,
2.92; N, 9.80.
II.J. Alternative Synthesis of 8. A solution of 5 (0.100 g, 0.361
mmol) in dichloromethane (5 mL) was added dropwise to a stirring
solution of (COD)PdCl2 (0.103 g, 0.361 mmol) in dichloromethane (10
mL). The solution became red-brown immediately upon addition. The
reaction solution was stirred at 62 °C for 24 h, after which time it was
cooled and dried in vacuo. The red solid was washed successively with
ethanol (3 × 10 mL), diethyl ether (2 × 10 mL), and pentane (2 × 10
mL) and then dried thoroughly under reduced pressure to yield a red
solid (114 mg, 77%). Spectral data were analogous with those reported
above.
II.F. Synthesis of [Tl][BQA], 6. [Li][BQA] (500 mg, 1.803 mmol)
and thallium triflate (637 mg, 1.803 mmol) were dissolved separately
in THF (25 mL) and cooled to -30 °C. The thallium triflate was then
added to the [Li][BQA] quickly, and the solution was stirred for 48 h
at ambient temperature. THF was removed in vacuo, and the resulting
red residue was extracted with benzene, filtered through Celite, and
dried by benzene lyophilization to afford a red powder. The crude
product was washed with petroleum ether (5 × 30 mL) and dried to
afford 6 (454 mg, 53%). The product contained trace impurities of
LiOTf, the complete removal of which has thus far proved problematic.
1H and 13C NMR, in addition to an X-ray diffraction study of a single
crystal obtained by vapor diffusion of petroleum ether into a benzene
solution, all support the assignment of the thallium complex 6. 1H NMR
(C6D6, 300 MHz, 25 °C): δ 8.09 (br s, 2H), 7.72 (d, J ) 7.5 Hz, 2H),
7.51 (d, J ) 8.4 Hz, 2H), 7.29 (m, 2H), 6.81 (d, J ) 7.8 Hz, 2H), 6.70
(br s, 2H). 13C NMR (C6D6, 75 MHz, 25 °C): δ 154.9, 145.7, 144.6,
137.8, 132.5, 127.9, 121.0, 114.9, 114.1.
II.K. Synthesis of (BQA)NiCl, 9. A 200 mL reaction bomb was
charged with 5 (200 mg, 0.722 mmol) dissolved in THF (50 mL). A
slurry of (DME)NiCl2 in THF (10 mL) was added to the stirring purple
solution. The solution began to turn red immediately upon addition.
The vessel was sealed with a Teflon stopcock and heated at 62 °C for
20 h. The reaction solution was allowed to cool, and the solvent was
removed in vacuo. The resulting red solid was washed with Et2O (50
mL), and LiCl was removed by extraction with EtOH (4 × 30 mL)
followed by Et2O (2 × 10 mL). The product was dried for 24 h under
reduced pressure to yield a microcrystalline red solid (220 mg, 84%).
Complex 9 may be recrystallized from a hexanes/chloroform diffusion
1
chamber. H NMR (CDCl3, 300 MHz, 25 °C): δ 8.66 (d, J ) 5 Hz,
2H), 8.13 (d, J ) 8 Hz, 2H), 7.49 (d, J ) 8 Hz, 2H), 7.40 (m, 2H),
7.27 (m, 2H), 6.95 (d, J ) 8 Hz, 2H). 13C NMR (CDCl3, 75 MHz, 25
°C): δ 150.6, 148.0, 147.8, 138.7, 129.8, 129.5, 121.3, 114.0, 111.7.
LR-MS (electrospray): calcd for C18H12ClN3Ni (M)+ m/z 363, found
(M - Cl)+ m/z 328. Anal. Calcd for C18H12N3ClNi: C, 59.32; H, 3.32;
N, 11.53. Found: C, 59.19; H, 3.31; N, 11.33.
II.L. Alternative Synthesis of 9. Ligand 1 (0.123 g, 0.455 mmol)
and (DME)NiCl2 (0.100 g, 0.455 mmol) were dissolved in THF (10
mL) at ambient temperature. An aliquot of triethylamine (190 µL, 1.365
mmol) was added in one portion. Within several minutes, the reaction
solution became red. Stirring was continued at 62 °C for 24 h. The
resulting red solution was cooled and dried in vacuo. The solid product
was then washed successively with ethanol (3 × 10 mL), diethyl ether
(2 × 10 mL), and pentane (2 × 10 mL) and dried under reduced
pressure for 24 h to yield 9 (147 mg, 89%). Spectral data were consistent
with those reported above.
II.M. Synthesis of (o-(NMe2)Ph-QA)Pt(1,2-η2-6-σ-cycloocta-1,4-
dienyl), 10. A 2 mL CH2Cl2 solution of (0.0706 g, 0.268 mmol) and
NEt3 (0.0814 g, 0.804 mmol) was added dropwise to a stirring solution
of (COD)PtCl2 (0.100 g, 0.268 mmol) in 3 mL of CH2Cl2. The reaction
gradually turned red in color and was allowed to stir for 24 h at rt,
after which time the volatiles were removed in vacuo. The resulting
crude red solid was then dissolved in 5 mL of benzene, filtered, and
lyophilized. Trituration with petroleum ether (3 × 3 mL) followed by
drying in vacuo yielded the analytically pure product (0.148 g, 98%)
as a mixture of two spectroscopically observable isomers in a 3:1 ratio
(vide infra). X-ray quality crystals were grown by vapor diffusion of
petroleum ether into a benzene solution of 10. Because of overlapping
resonances resulting from the two isomers, it was not possible to reliably
II.G. Synthesis of (BQA)PtCl, 7. A benzene solution (20 mL) of
[Li][BQA] (370.5 mg, 1.336 mmol) was quickly added to a flask
containing (COD)PtCl2 (500 mg, 1.336 mmol) dissolved in benzene
(30 mL) that had been chilled to -35 °C. The stirring reaction solution
was allowed to warm slowly and was subsequently heated at 65 °C for
an additional 20 h. The resulting intense purple solution was filtered
through Celite, followed by additional washings with dichloromethane
(3 × 10 mL). Solvent was removed from the filtrate in vacuo. The
resulting purple solid was washed with petroleum ether (3 × 30 mL)
and dried, affording a purple powder (454 mg, 68%). This powder was
easily recrystallized in a hexane/chloroform diffusion chamber. 1H NMR
(CDCl3, 300 MHz, 25 °C): δ 9.14 (d, J ) 5.0 Hz, 2H, 3JPtH ) 37 Hz),
8.23 (d, J ) 8.3 Hz, 2H), 7.62 (d, J ) 8.0 Hz, 2H), 7.43 (m, 2H), 7.37
(m, 2H), 7.02 (d, J ) 8.4 Hz, 2H). 13C NMR (CDCl3, 75 MHz, 25
°C): δ 148.8, 148.7, 148.4, 138.9, 131.4, 129.4, 121.2, 115.7, 113.6.
LR-MS (electrospray): calcd for C18H12ClN3Pt (M)+ m/z 500, found
(M + H)+ m/z 501. Anal. Calcd for C18H12ClN3Pt: C, 43.17; H, 2.42;
N, 8.39. Found: C, 42.81; H, 2.47; N, 8.03.
II.H. Alternative Synthesis of 7. To a reaction vessel containing 1
(1.00 g, 3.6 mmol) and (COD)PtCl2 (1.346 g, 3.6 mmol) dissolved in
THF (30 mL), triethylamine (651 µL, 4.68 mmol) was added in one
portion. The vessel was sealed and stirred at 95 °C for 48 h. The
resulting red solution was cooled and dried in vacuo, extracted with
CH2Cl2 (50 mL), and filtered through Celite on a sintered-glass frit.
The solvent was again removed under reduced pressure, and the
precipitate was washed with methanol (3 × 30 mL) and petroleum
ether (2 × 10 mL) and then dried in vacuo to give the desired product
(1.176 g, 65%). Spectral data were consistent with those reported above.
1
1
II.I. Synthesis of (BQA)PdCl, 8. To a reaction flask containing
(COD)PdCl2 (1.05 g, 3.6 mmol) dissolved in THF (75 mL) was added
a THF solution of 1 (1.00 g, 3.6 mmol) and triethylamine (651 µL,
4.68 mmol). The vessel was sealed and heated at 95 °C for 48 h. After
the reaction was cooled, the reaction solution volatiles were removed
in vacuo, affording a red residue. This crude product was dissolved in
CH2Cl2 (50 mL), filtered through Celite on a sintered-glass frit, and
washed with dilute brine solution (3 × 20 mL). The volume was
reduced in vacuo, and the product was precipitated from solution with
hexanes. The resulting red microcrystalline solid was washed with
integrate the H NMR spectrum. The observed resonances for the H
and 13C NMR are reported. H NMR (CDCl3, 300 MHz, 25 °C): δ
1
3
8.20 (dd, J ) 1.0, 8.0 Hz), 8.04 (dd, J ) 1.0, 4.8 Hz, JPtH ) 17 Hz),
2
6.93-7.45 (m), 6.76 (m), 6.31 (m), 5.53 (m), 5.34 (m), 4.93 (m, JPtH
2
) 72 Hz), 4.62 (m, JPtH ) 72 Hz), 3.57 (m), 3.00-3.2 (m), 2.77 (m,
NMe2, major isomer), 2.72 (m, NMe2, minor isomer), 1.20-2.0 (m).
13C NMR (CDCl3, 75 MHz, 25 °C): δ 156.9, 149.3, 141.9, 142.2, 141.7,
138.0, 135.8, 135.4, 133.9, 130.5, 130.4, 130.3, 130.2, 129.4, 129.0,
128.3, 126.8, 125.2, 121.5, 121.2, 121.0, 120.9, 118.2, 117.4, 110.7,
110.6, 109.9, 76.7, 71.0, 53.3, 46.4, 43.7, 42.8, 40.9, 40.4, 40.2, 36.4,

5086 Inorganic Chemistry, Vol. 40, No. 20, 2001
Peters et al.
33.7, 31.7, 28.9, 28.7, 28.3, 27.0, 25.6, 25.0, 24.9, 9.29, 8.50. LR-MS
(electrospray): calcd for C25H27N3Pt (M)+ m/z 564, found (M + H)+
m/z 565. Anal. Calcd for C25H27N3Pt: C, 53.18; H, 4.82; N, 7.44.
Found: C, 53.45; H, 4.75; N, 7.19.
KR) ) 0.71073 Å, T ) 98(2) K, Bruker SMART 1000 CCD, crystal
size ) 0.28 × 0.22 × 0.22 mm3, θmax ) 28.31°, R1 ) 0.0245, wR2 )
0.0452, for I > 2σ(I) R1 ) 0.0331, wR2 ) 0.0460, number of
reflections collected ) 26365 (-11 e h e 12, -14 e k e 15, -19 e
l e 19), number of independent reflections ) 3635, number of
parameters ) 256.
II.N. Synthesis of (3,5-Me2Ph-QA)Pt(1,2-η2-6-σ-cycloocta-1,4-
dienyl), 11. A 2 mL CH2Cl2 solution of 4 (0.0666 g, 0.268 mmol) and
NEt3 (0.0814 g, 0.804 mmol) was added dropwise to a stirring solution
of (COD)PtCl2 (0.100 g, 0.268 mmol) in 3 mL of CH2Cl2. The reaction
gradually turned red in color and was allowed to stir for 24 h at rt,
after which time the volatiles were removed in vacuo. The resulting
crude red solid was then dissolved in 5 mL of benzene, filtered, and
lyophilized. Trituration with petroleum ether (3 × 3 mL) followed by
drying in vacuo yielded a spectroscopically pure product (0.140 g, 95%).
X-ray quality crystals were grown from vapor diffusion of petroleum
II.R. X-ray Crystal Structure Analysis of (BQA)PdCl, 8. X-ray
quality crystals were obtained from a chloroform/petroleum ether
diffusion chamber at 25 °C. A dark red crystalline column was mounted
on a glass fiber with Paratone-N oil. The structure was solved by direct
methods in conjunction with standard difference Fourier techniques.
The largest peak and hole in the difference map were 0.587 and -0.522
e Å-3, respectively. No data correction was applied. Maximum and
minimum transmissions were equal to 0.7428 and 0.6828, respectively.
Crystal data for C18H12ClN3Pd: monoclinic space group P21/n (No.
14), a ) 7.5343(7) Å, b ) 14.9983(14) Å, c ) 12.8184(12) Å, â )
93.845(2)°, V ) 1445.2(2) Å3, Z ) 4, Dcalcd ) 1.894 g cm-3, abs
coefficient ) 1.470 mm-1, λ(Mo KR) ) 0.71073 Å, T ) 98(2) K,
Bruker SMART 1000 CCD, crystal size ) 0.28 × 0.22 × 0.22 mm3,
θmax ) 28.06°, R1 ) 0.0267, wR2 ) 0.0544, for I > 2σ(I) R1 ) 0.0318,
wR2 ) 0.0549, number of reflections collected ) 20400 (-9 e h e
9, -18 e k e 19, -16 e l e 16), number of independent reflections
) 3343, number of parameters ) 256.
1
ether into benzene. H NMR (CDCl3, 300 MHz, 25 °C): δ 8.20 (dd,
3
J ) 1.0, 8.4 Hz, 1H), 8.05 (dd, J ) 1.0, 4.5 Hz, 1H, JPtH ) 17 Hz),
7.41 (m, 1H), 7.25 (m, 1H), 6.87 (s, 2H), 6.83 (s, 1H), 6.77 (d, J ) 8.1
Hz, 1H), 6.60 (d, J ) 8.1 Hz, 1H), 5.54 (m, 1H), 5.36 (m, 1H), 4.97
2
2
(m, 1H, JPtH ) 72 Hz), 4.65 (m, 1H, JPtH ) 72 Hz), 3.16 (m, 1H),
2.80 (m, 1H), 2.35 (s, 6H), 2.00-1.32 (m, 5H). 13C NMR (CDCl3, 75
MHz, 25 °C): δ 159.1, 150.4, 142.1, 138.5, 138.0, 135.5, 131.2, 130.4,
129.0, 128.5, 125.9, 125.7, 121.2, 111.1, 109.5, 77.2, 70.7, 41.0, 31.5,
28.8, 24.9, 21.8. LR-MS (electrospray): calcd for C25H26N2Pt (M)+
m/z 549, found (M + H)+ m/z 550. Anal. Calcd for C25H26N2Pt: C,
54.64; H, 4.77; N, 5.10. Found: C, 54.61; H, 5.01; N, 4.99.
II.S. X-ray Crystal Structure Analysis of (BQA)NiCl, 9. X-ray
quality crystals were obtained from a chloroform/hexanes diffusion
chamber at 25 °C. A dark red crystalline block was mounted on a glass
fiber with Paratone-N oil. The structure was solved by direct methods
in conjunction with standard difference Fourier techniques. The largest
II.O. X-ray Crystal Structure Analysis of [Li][BQA], 5. X-ray
quality crystals were obtained from a benzene/petroleum ether diffusion
chamber at 25 °C. A red crystalline blade was mounted on a glass
fiber with Paratone-N oil (an Exxon product). The structure was solved
by direct methods in conjunction with standard difference Fourier
techniques. The largest peak and hole in the difference map were 0.351
and -0.195 e Å-3, respectively. Maximum and minimum transmissions
were equal to 0.9971 and 0.9684, respectively. Crystal data for C36H24-
Li2N6: monoclinic space group P21/c (No. 14), a ) 22.490(3) Å, b )
8.6035(10) Å, c ) 14.4810(17) Å, â ) 97.875(2)°, V ) 2775.5(6) Å3,
Z ) 4, Dcalcd ) 1.327 g cm-3, abs coefficient ) 0.079 mm-1, λ(Mo
KR) ) 0.710 73 Å, T ) 98(2) K, Bruker SMART 1000 CCD, crystal
size ) 0.41 × 0.3 × 0.04 mm3, θmax ) 28.36°, R1 ) 0.0525, wR2 )
0.0835, for I > 2σ(I) R1 ) 0.1141, wR2 ) 0.0877, number of
reflections collected ) 39470 (-29 e h e 29, -11 e k e 11, -19 e
l e 18), number of independent reflections ) 6569, number of
parameters ) 493.
peak and hole in the difference map were 0.309 and -0.377 e Å-3
,
respectively. Maximum and minimum transmissions were equal to
0.7535 and 0.7213, respectively. Crystal data for C18H12ClN3Ni:
monoclinic space group P21/n (No. 14), a ) 8.9635(7) Å, b )
11.4785(9) Å, c ) 14.9909(12) Å, â ) 107.3220(10)°, V ) 1472.4(2)
Å3, Z ) 4, Dcalcd ) 1.644 g cm-3, abs coefficient ) 1.500 mm-1, λ(Mo
KR) ) 0.71073 Å, T ) 98(2) K, Bruker SMART 1000 CCD, crystal
size ) 0.23 × 0.20 × 0.20 mm3, θmax ) 28.26°, R1 ) 0.0317, wR2 )
0.0615, for I > 2σ(I) R1 ) 0.0426, wR2 ) 0.0627, number of
reflections collected ) 20863 (-11 e h e11, -15 e k e 14, -19 e
l e 19), number of independent reflections ) 3452, number of
parameters ) 256.
II.T. X-ray Crystal Structure Analysis of (o-(NMe2)Ph-QAH)-
Pt(1,2-η2-6-σ-cycloocta-1,4-dienyl), 10a. X-ray quality crystals were
obtained from a benzene/petroleum ether diffusion chamber at 25 °C.
A red crystalline block was mounted on a glass fiber with Paratone-N
oil. The structure was solved by direct methods in conjunction with
standard difference Fourier techniques. The largest peak and hole in
the difference map were 1.488 and -0.577 e Å-3, respectively.
Maximum and minimum transmissions were equal to 1.0000 and
0.7282, respectively. Crystal data for C25H27N3Pt: triclinic space group
P1h (No. 2), a ) 7.5521(7) Å, b ) 10.7997(9) Å, c ) 13.4693(12) Å,
R ) 108.3110(10)°, â ) 107.3220(10)°, γ ) 94.7070(10)°, V )
1034.23(16) Å3, Z ) 2, Dcalcd ) 1.813 g cm-3, abs coefficient ) 6.800
mm-1, λ(Mo KR) ) 0.71073 Å, T ) 98(2) K, Bruker SMART 1000
CCD, crystal size ) 0.22 × 0.19 × 0.15 mm3, θmax ) 28.31°, R1 )
0.0237, wR2 ) 0.0413, for I > 2σ(I) R1 ) 0.0204, wR2 ) 0.0410,
number of reflections collected ) 15396 (-9 e h e10, -14 e k e
14, -17 e l e 17), number of independent reflections ) 4745, number
of parameters ) 370.
II.P. X-ray Crystal Structure Analysis of [Tl][BQA], 6. X-ray
quality crystals were obtained from a benzene/petroleum ether diffusion
chamber at 25 °C. A red crystalline blade was mounted on a glass
fiber with Paratone-N oil. The structure was solved by direct methods
in conjunction with standard difference Fourier techniques. The largest
peak and hole in the difference map were 1.738 and -1.191 e Å-3
,
respectively. SADABS data correction was applied on the basis of
pseudo-ψ scans with maximum and minimum transmissions equal to
0.7535 and 0.7213, respectively. Crystal data for C18H12N3Tl: ortho-
rhombic space group Pna21 (No. 33), a ) 6.9767(11) Å, b ) 23.289(4)
Å, c ) 8.7724(13) Å, V ) 1425.3(4) Å3, Z ) 4, Dcalcd ) 2.212 g cm-3
,
abs coefficient ) 11.330 mm-1, λ(Mo KR) ) 0.710 73 Å, T ) 98(2)
K, Bruker SMART 1000 CCD, crystal size ) 0.89 × 0.23 × 0.16
mm3, θmax ) 28.39°, R1 ) 0.0245, wR2 ) 0.0397, for I > 2σ(I) R1
) 0.0336, wR2 ) 0.0405, number of reflections collected ) 22995
(-9 e h e 8, -29 e k e 30, -11 e l e 11), number of independent
reflections ) 3324, number of parameters ) 199.
II.U. X-ray Crystal Structure Analysis of (3,5-Me2Ph-QA)Pt(1,2-
η2-6-σ-cycloocta-1,4-dienyl), 11. X-ray quality crystals were obtained
from a benzene/petroleum ether diffusion chamber at 25 °C. A red
crystalline block was mounted on a glass fiber with Paratone-N oil.
The structure was solved by direct methods in conjunction with standard
difference Fourier techniques. The largest peak and hole in the
difference map were 1.357 and -0.496 e Å-3, respectively. Maximum
and minimum transmissions were equal to 1.0000 and 0.6946,
respectively. Crystal data for C25H26N2Pt: orthorhombic space group
P212121, a ) 9.2884(7) Å, b ) 11.4127(9) Å, c ) 19.3116(12) Å, V )
2047.1(3) Å3, Z ) 4, Dcalcd ) 1.783 g cm-3, abs coefficient ) 6.867
mm-1, λ(Mo KR) ) 0.71073 Å, T ) 98(2) K, Bruker SMART 1000
II.Q. X-ray Crystal Structure Analysis of (BQA)PtCl, 7. X-ray
quality crystals were obtained from a chloroform/petroleum ether
diffusion chamber at 25 °C. A dark red crystalline column was mounted
on a glass fiber with Paratone-N oil. The structure was solved by direct
methods in conjunction with standard difference Fourier techniques.
The largest peak and hole in the difference map were 1.015 and -0.976
e Å-3, respectively. SADABS data correction was applied on the basis
of pseudo-ψ scans with maximum and minimum transmissions equal
to 1.0000 and 0.5322, respectively. Crystal data for C18H12ClN3Pt:
monoclinic space group P21/n (No. 14), a ) 9.1532(12) Å, b )
11.5481(15) Å, c ) 15.1060(19) Å, â ) 106.997(2)°, V ) 1527.0(3)
Å3, Z ) 4, Dcalcd ) 2.179 g cm-3, abs coefficient ) 9.365 mm-1, λ(Mo

Amido Complexes of Pt, Pd, and Ni
Inorganic Chemistry, Vol. 40, No. 20, 2001 5087
CCD, crystal size ) 0.29 × 0.13 × 0.07 mm3, θmax ) 28.46°, R1 )
0.0210, wR2 ) 0.0347, for I > 2σ(I) R1 ) 0.0192, wR2 ) 0.0344,
number of reflections collected ) 30635 (-12 e h e 12, -14 e k e
15, -25 e l e 25), number of independent reflections ) 4878, number
of parameters ) 335.
Scheme 1
III. Results and Discussion
III.A. Preparation of Ligands. A synthetic strategy for the
preparation of amines 1-4 exploits Pd-coupling methodology
for N-C bond formation, a transformation that has recently
matured because of the efforts of the respective research groups
of Buchwald and Hartwig.20 A new synthesis of the previously
prepared amine 1 provided a good starting point for several
reasons. First, in our hands, the literature preparation of 1
afforded unacceptably low yields (typically less than 10%) of
the desired product ligand and was simultaneously time-
consuming and very tedious.11 Direct coupling of commercially
available 8-aminoquinoline with 8-bromoquinoline promised to
be a more elegant preparation of 1 in comparison to the low-
yielding Bucherer reaction by which it was originally synthe-
sized. Second, although 1 was first prepared nearly four decades
ago, only a single transition metal complex, (BQA)CuCl,11 has
been definitively characterized supported by this potentially
versatile auxiliary ligand. We anticipated that 1 and related
amines would yield to a rich reaction chemistry among the
transition elements and hence set about its improved preparation.
It was found that the reaction between 8-bromoquinoline and
8-aminoquinoline under standard coupling conditions (Pd2(dba)3,
toluene, 110 °C) with NaOtBu as the base and rac-BINAP as
the cocatalyst provided reliably high yields of 1. The product
was readily isolated by flash chromatography and analyzed by
manuscript, provides two symmetrical quinolinyl donor arms
capable of forming two fused five-membered rings upon
metalation. This motif has now been structurally established
for several square-planar (vide infra) and octahedral complexes
of 1.22
1
LR-MS and H and 13C NMR spectroscopies. The data for 1
compared favorably with those for 1 obtained by its independent
preparation following the literature procedure.11 Ligand 1 has
been prepared on multigram scales in isolated yields typically
greater than 80%. A catalyst loading of 2-4% is sufficient: an
isolated yield of 94% has been obtained with a 4% catalyst
loading. Notably, 1, while an excellent chelating ligand for
palladium (vide infra), does not poison the catalyst system.
III.B. Preparation and Structural Characterization of
the Lithium and Thallium Derivatives, [Li][BQA] (5) and
[Tl][BQA] (6). To explore the coordination chemistry of 1, we
first sought a reliable preparative procedure for its lithiation.
Of immediate concern to us was that employment of the typical
nBuLi base for deprotonation might result in competitive
nucleophilic attack at the relatively electrophilic 2-carbon
position of the quinoline ring. Indeed, when a stoichiometric
Hoping to extend this methodology to three related amines,
we attempted the synthesis of 2-pyridin-2-yl-ethyl-QAH (2),
o-(NMe2)Ph-QAH (3), and 3,5-Me2Ph-QAH (4) under the same
conditions.21 The reaction worked well for 2 but proved sluggish
for 3 and 4. A survey of other cocatalysts established DPPF
(DPPF ) bis(diphenylphosphino)ferrocene) as a viable alterna-
tive for the preparation of both 3 and 4 in satisfactory isolated
yield after flash chromatography. The syntheses for ligands 1-4
are summarized in Scheme 1. These anionic amido ligands are
related in that each can provide a metal atom with one amido
N-donor group and one or two neutral nitrogen donor groups.
Ligand 1, the chemistry of which is the primary focus of this
n
amount of BuLi is added slowly to a toluene solution of 1 at
ambient temperature, significant side products result from
competitive alkylation; these byproducts are difficult to separate
from the major product, 5. Fortunately, slow dropwise addition
of a dilute solution of nBuLi to 1 at -78 °C circumvents
kinetically competitive alkylation products, and the intensely
orange lithium complex 5 is formed cleanly in the absence of
donor solvent (Scheme 2). The amide 5 is unusual in that it is
both soluble and stable in halogenated solvents such as
chloroform and methylene chloride.
To examine its solid-state structure, crystals suitable for an
X-ray diffraction study were obtained by slow diffusion of
petroleum ether into a benzene solution. The structure of 5,
shown in Figure 1, shows a dimeric complex in which two
lithium cations, LiA and LiB, and two bridging amido nitrogens,
N(2A) and N(2B), join to form a parallelepiped that bisects the
dimeric molecule. Each of the two donor quinolinyl arms of
the amido ligands binds a different lithium cation, imparting a
twisted structure to the molecule, the idealized molecular
(20) (a) Wolfe, J. P.; Tomori, H.; Sadighi, J. P.; Yin, J. J.; Buchwald, S.
L. J. Org. Chem. 2000, 65, 1158. (b) Alcazar-Roman, L. M.; Hartwig,
J. F.; Rheingold, A. L.; Liable-Sands, L. M.; Guzei, I. A. J. Am. Chem.
Soc. 2000, 122, 4618. (c) Hartwig, J. F. Acc. Chem. Res. 1998, 31,
852. (d) Hamamm, B. C.; Hartwig, J. F. J. Am. Chem. Soc. 1998,
120, 12706.
(21) In this manuscript we have adopted the following simplification for
naming ligands 1-4: The ligands are all derived from the primary
amine 8-quinolinylamine (abbreviated as QAH in this manuscript).
The second substituent at nitrogen, affording the secondary amine, is
written explicitly in conjunction with QAH. Thus, (o-NMe2Ph-QAH)
implies that 8-aminoquinoline is substituted by an aryl group containing
a dimethylamino group in the ortho position. When bound to a metal
as an anionic amido ligand, the H is dropped from QAH, as in
(BQA)PtCl.
(22) Betley, T.; Brown, S. D.; Harkins, S. B.; Qian, B.; Peters, J. C.
Unpublished results.

5088 Inorganic Chemistry, Vol. 40, No. 20, 2001
Peters et al.
Figure 2. Displacement ellipsoid (50%) representation of [Tl][BQA]
(6). Selected bond distances (Å) and angles (deg) are as follows: Tl-
N(2), 2.397(4); Tl-N(1), 2.689(4); Tl-N(3), 2.802(5); N(2)-Tl-N(1),
63.98(13); N(2)-Tl-N(3), 63.20(15); N(1)-Tl-N(3), 124.98(13);
C(8)-N(2)-C(17), 121.6(4); C(9)-N(1)-Tl, 110.8(3); C(18)-N(3)-
Tl, 105.7(3); C(1)-N(1)-Tl, 125.0(3); C(8)-N(2)-Tl, 121.0(3);
C(17)-N(2)-Tl, 117.1(3).
Figure 1. Displacement ellipsoid (50%) representation of [Li][BQA]
(5). Selected bond distances (Å) and angles (deg) are as follows: LiA-
N(1A), 2.024(4); LiA-N(2A), 2.079(4); LiA-N(2B), 2.063(4); LiA-
N(3B), 1.990(4); LiA-LiB, 2.395(5); LiB-N(1B), 1.958(4); LiB-
N(2B), 2.051(4); LiB-N(2A), 2.018(4); LiB-N(3A), 1.999(4); N(2B)-
LiA-N(2A), 107.15(18); N(2A)-LiA-LiB, 53.05(13); N(2B)-LiA-
LiB, 54.16(13); N(2B)-LiA-N(2A), 107.15(18); N(1A)-LiA-N(2A),
82.50(15); N(3B)-LiA-N(2A), 103.80(17); C(8A)-N(2A)-C(17A),
120.37(17).
Scheme 2
symmetry of which is D2. The quinoline donor arms of each
amido ligand are appreciably canted, and the average angle of
intersection defined by their respective mean planes is 58.43°.
A simple molecular mechanics minimization of its protonated
form, BQAH, predicts an intersection angle of approximately
50°.
Figure 3. Displacement ellipsoid (50%) representation of [Tl][BQA]
(6) extended along the crystallographic a-axis. The shaded ellipsoids
are connected in a zigzag chain highlighting the Tl cations (Tl-Tl1 )
3.5336(5) Å).
While a host of amide complexes of thallium(III) have been
reported, stable and well-defined examples of thallium(I) amides
are exceedingly rare. The only well-characterized example of
which we are aware, TlN(SiMe3)2, is dimeric in the crystalline
state.23,24 The chelating amido ligand 1 presented a good
candidate for supporting a rigorously monomeric thallium(I)
amide. Direct exchange of thallium for lithium was effected by
addition of TlOTf to a THF solution of 5. LiOTf precipitated
upon benzene extraction of the red residue, and the new red
product, [Tl][BQA] (6), was isolated and determined to be free
and a Tl cation (Figure 2). A possible weak π-stacking or Tl-
Tl interaction is observable in the extended structure (Figure
3). Notably, the nearest neighbor Tl cation is located at a
distance of 3.5336(5) Å, significantly longer than a generous
estimate of the sum of the ionic radii for two Tl(I) cations (ca.
3.28 Å for coordination number of 6).25 The thallium complexes
stack in adjacent columns, each column containing a repeat
zigzag arrangement of the monomeric unit. Because of its
solubility in benzene, we presume that this zigzag chain structure
of 6 in the crystalline state is not present in solution and that 6
is best regarded as a monomeric amido complex of thallium(I).26
Important to note is that the BQA ligand, which at first glance
might seem to have a small binding pocket, is able to
accommodate the very large Tl(I) cation in a well-defined,
tridentate fashion. The ligand appears to accommodate this
1
of starting material 5 by H NMR spectroscopy. An X-ray
diffraction study of a single crystal of 6 established that the
desired Tl(I) complex of the BQA ligand was indeed the species
formed. The X-ray structure of 6 shows a discrete, monomeric
complex with a one-to-one adduct between the η3-BQA ligand
(23) Klinkhammer, K. W.; Henkel, S. J. Organomet. Chem. 1994, 480,
167.
(24) This complex was assigned as a monomer in the gas phase. See:
Haaland, A.; Shorokhov, D. J.; Volden, H. V.; Klinkhammer, K. W.
Inorg. Chem. 1999, 38, 1118.
(25) Shannon, R. D. Acta Crystallogr. 1976, A32, 751.

Amido Complexes of Pt, Pd, and Ni
Inorganic Chemistry, Vol. 40, No. 20, 2001 5089
Figure 4. Displacement ellipsoid (50%) representations of the divalent (BQA)MCl complexes 7-9 (M ) Pt, Pd, and Ni, respectively). Two views
are depicted for each structure. The top view is perpendicular to the square plane and the bottom view looks down the Cl-M-N2 axis. Selected
bond distances (Å) and angles (deg) are as follows. (BQA)PtCl (7): Pt-N(2), 1.966(3); Pt-N(1), 1.994(3); Pt-N(3), 1.999(3); Pt-Cl, 2.3175(11);
N(1)-Pt-N(3), 165.34(13); C(17)-N(2)-C(8), 130.9(3); N(2)-Pt-Cl, 177.40(9); N(2)-Pt-N(1), 82.74(12); N(2)-Pt-N(3), 82.70(12); N(1)-
Pt-Cl, 97.55(10); N(3)-Pt-Cl, 97.07(10). (BQA)PdCl (8): Pd-N(2), 1.962(2); Pd-N(3), 2.0017(19); Pd-N(1), 2.0114(19); Pd-Cl, 2.3298(7);
N(2)-Pd-N(3), 82.58(8); N(2)-Pd-N(1), 82.53(8); N(3)-Pd-N(1), 165.10(8); N(2)-Pd-Cl, 178.03(6); N(3)-Pd-Cl, 96.41(6); N(1)-Pd-Cl,
98.45(6); C(17)-N(2)-C(8), 130.4(2); C(17)-N(2)-Pd, 114.81(15); C(8)-N(2)-Pd, 114.53(15); C(18)-N(3)-Pd, 111.71(15). (BQA)NiCl (9):
Ni-N(2), 1.8586(14); Ni-N(3), 1.8973(16); Ni-N(1), 1.8973(16); Ni-Cl, 2.1779(5); N(2)-Ni-N(3), 84.70(6); N(2)-Ni-N(1), 84.60(6); N(3)-
Ni-N(1), 169.10(6); N(2)-Ni-Cl, 174.77(5); N(3)-Ni-Cl, 95.62(5); N(1)-Ni-Cl, 95.23(5); C(1)-N(1)-Ni, 129.25(15); C(8)-N(2)-C(17),
129.05(15); C(8)-N(2)-Ni, 115.49(11); C(17)-N(2)-Ni, 115.43(12); C(10)-N(3)-Ni, 128.84(14); C(18)-N(3)-Ni, 112.42(12).
Scheme 3
with benzene and filtering it away from Et3N‚HCl. Alternatively,
7 can be prepared by transmetalation with [Li][BQA] in benzene
at 65 °C. Complex 7 is an intensely purple solid that is both air
and water stable. The complexes (BQA)PdCl (8) and (BQA)-
NiCl (9) were prepared by similar methods from (COD)PdCl2
and Ni(DME)Cl2 (DME ) dimethoxyethane), respectively.
These reactions are summarized in Scheme 3.
III.D. X-ray Structural Study of (BQA)MCl (M ) Ni, Pd,
Pt). We undertook a comparative X-ray diffraction study of
complexes 7-9 to determine the adopted BQA ligand geometry
for divalent group 10 metal ions.10 All three complexes
crystallized in the space group P21/n and, as expected, formed
monomeric, square-planar structures. As can be seen in Figure
4, all three complexes are highly planar. Complexes 7 and 8
are virtually isostructural. Notably, the N3-M-N1 angle
decreases on going from Ni (169.3°) to Pd and Pt (av ) 165.2°),
reflecting a configurational adjustment when the larger divalent
ions are accommodated. This change is not reflected in the C8-
N2-C17 angle about the amido nitrogen donor, which in fact
slightly increases (ca. 2°) for Pd and Pt relative to Ni.
III.E. Comparing the Reactivity of (COD)PtCl2 with the
Potentially Tridentate Ligands 2-Pyridine-2-yl-ethyl-QAH
(2) and o-(NMe2)Ph-QAH (3) and the Bidentate Ligand 3,5-
Me2Ph-QAH (4). Having established that the parent BQA
ligand coordinates platinum(II) in a rigorously tridentate fashion,
we attempted the preparation of analogous complexes bearing
the potentially tridentate ligands 2 and 3. While reaction of 2
with (COD)PtCl2 afforded an ill-defined product mixture,27
addition of a stoichiometric amount of 3 to (COD)PtCl2 in the
presence of excess triethylamine base effected a rapid color
change with concurrent salt precipitation. A 1H NMR spectrum
of the isolated crystalline product, however, showed two
resonances attributable to dimethylamino groups in about a 3:1
ratio; no coalescence was observed on raising the temperature
to 80 °C. Resonances originating from a COD-like ligand were
also present, establishing that simple displacement of cyclo-
octadiene had not occurred. Despite successive recrystallizations,
unusually large ion by canting its two quinolinyl arms in such
a fashion that the intersection angle of the two planes defined
by the quinoline planes is 57.46(11)°. However, this intersection
angle is analogous to that found for the lithium dimer 5. Thus,
transmetalation of the small lithium cation for the much larger
thallium cation actually effects little conformational change in
the ligand morphology. As will be discussed below, this BQA
geometry markedly contrasts with that found for the divalent,
square-planar complexes of Ni, Pd, and Pt and the previously
characterized square-planar copper(II) complex.11
III.C. Preparation of Divalent Ni, Pd, and Pt Complexes
of BQA Ligand 1. The two methods that proved efficacious
for the preparation of divalent monochloride complexes of the
group 10 metals supported by BQA were (i) transmetalation
with the [Li][BQA] reagent and (ii) dehydrohalogenation using
the free acid BQAH in the presence of NEt3 base. For example,
reaction of BQAH/NEt3 with (COD)PtCl2 in methylene chloride
solution generates (BQA)PtCl (7) quantitatively with concomi-
tant liberation of cyclooctadiene. Removal of the hydrochloride
salt byproduct was accomplished either by ethanol washing of
the alcohol insoluble product or by extracting the target complex
(26) One caveat regarding the preparation of 6 needs to be noted. Although
suitable crystals were obtained for the X-ray analysis, 1H, 13C, and
19F NMR spectra of recrystallized samples of 6, while showing only
one BQA-containing species, consistently show trace amounts of THF
and triflate anion, which we presume to result from some ill-defined
association of LiOTf. Efforts to fully remove these trace impurities,
including successive lyophilizations from frozen benzene followed by
hydrocarbon extraction and filtration, have thus far been unsuccessful,
preventing a successful combustion analysis.
(27) We tentatively assign the primary platinum-containing product of this
reaction as {2-pyridin-2-yl-ethyl-QA}Pt(1,2-η2-6-σ-cycloocta-1,4-di-
enyl), with ligand 2 binding in an η2-fashion analogous to the well-
characterized complexes 10a and 11 (vide supra). Unfortunately,
although LC-MS (ES) corroborates this assignment, its complete
isolation and purification has thus far eluded us.

5090 Inorganic Chemistry, Vol. 40, No. 20, 2001
Peters et al.
Figure 6. Displacement ellipsoid (50%) representation of (3,5-Me2Ph-
QA)Pt(1,2-η2-6-σ-cycloocta-1,4-dienyl) (11). Selected bond distances
(Å) and angles (deg) are as follows: Pt(1)-N(2), 2.008(3); Pt(1)-
C(18), 2.048(3); Pt(1)-C(22), 2.123(3); Pt(1)-C(23), 2.124(3); Pt(1)-
N(1), 2.135(3); C(18)-C(19), 1.486(5); C(18)-C(25), 1.549(5); C(19)-
C(20), 1.324(6); C(20)-C(21), 1.495(5); C(21)-C(22), 1.508(5);
C(22)-C(23), 1.395(5); C(23)-C(24), 1.512(5); C(24)-C(25), 1.519(5);
N(2)-Pt(1)-C(18), 96.77(12); N(2)-Pt(1)-C(22), 158.63(12); C(18)-
Pt(1)-C(22), 89.25(14); N(2)-Pt(1)-C(23), 162.98(13); C(18)-Pt(1)-
C(23), 80.62(14); N(2)-Pt(1)-N(1), 79.63(11); C(18)-Pt(1)-N(1),
175.07(13); C(22)-Pt(1)-N(1), 95.31(12); C(23)-Pt(1)-N(1),
101.83(12).
Figure 5. Displacement ellipsoid (50%) representation of (o-(NMe2)-
Ph-QA)Pt(1,2-η2-6-σ-cycloocta-1,4-dienyl) (10a). Selected bond dis-
tances (Å) and angles (deg) are as follows: Pt-N(2), 2.003(2); Pt-
C(18), 2.037(3); Pt-C(22), 2.115(3); Pt-N(1), 2.126(2); Pt-C(23),
2.141(3); C(18)-C(19), 1.489(5); C(18)-C(25), 1.537(5); C(19)-
C(20), 1.324(5); C(20)-C(21), 1.484(5); C(21)-C(22), 1.509(5);
C(22)-C(23), 1.395(5); C(23)-C(24), 1.523(5); C(24)-C(25), 1.524(5);
N(2)-Pt-C(18), 95.93(12); N(2)-Pt-C(22), 156.80(11); C(18)-
Pt-C(22), 89.60(13); N(2)-Pt-N(1), 79.45(10); C(18)-Pt-N(1),
171.50(11); C(22)-Pt-N(1), 97.43(11); N(1)-Pt-C(23), 102.22(12).
Scheme 4
we collected data on the second crystal type of the batch crystals.
The data set collected was difficult to solve and was best
interpreted as a mixture of two diastereomers in a 3:1 ratio, the
major diastereomer being analogous to the structure of 10b.28
Further direct evidence for the simple formulation of 10 as
the two spectroscopically distinct isomers 10a and 10b was
provided by the following data: (i) Combustion analysis of the
batch crystals was consistent with the simple empirical formula
of complex 10. (ii) Only one species ((M + H)+ ) 565) was
observed by LR-MS (electrospray; positive mode) for a batch
sample of complex 10 (FW ) 564). (iii) The same product was
obtained employing (COD)PtI2 instead of (COD)PtCl2 as the
platinum starting material. A space-filling model of 10b leads
us to conclude that facile rotation of the ortho-substituted aryl
ring about the N2-C10 axis is not possible, and thus, the two
diastereomers become spectroscopically distinct on the NMR
time scale. If this interpretation is correct, then preparation of
a bidentate ligand variation of 10 without an o-dimethylamino
group, as is the case for ligand 4, should lead to a single
spectroscopically observable product. Indeed, it was found that
when 4 was added to (COD)PtCl2 in the presence of excess
triethylamine, a single isomer was observed by 1H NMR
spectroscopy at 25 °C and was assigned as the product (3,5-
Me2Ph-QA)Pt(1,2-η2-6-σ-cycloocta-1,4-dienyl) (11). An X-ray
structural investigation of the crystallized product (Figure 6)
established that 11 has a structure analogous to that of 10a. In
the case of 11, we presume that facile rotation around the N2-
C10 axis is fast on the NMR time scale and equilibrates the
methyl positions on the aryl ring that are clearly chemically
distinct in the solid-state structure of 11. Taken collectively,
the data establish that ligands 3 and 4 react with (COD)PtCl2
to give similar products, 10 and 11, with the added complication
that complex 10 exists in solution as two observable dia-
stereomeric isomers.
there was no change in the relative intensities of the two
dimethylamino resonances implying that the reaction product
was likely a mixture of two isomers. On closer inspection of a
batch of isolated red crystals, it was determined that two
crystalline forms were present; an attempt was made to solve
the solid-state structure of each. One of the two crystal types
gave a high-quality data set, and its solid-state structure is shown
in Figure 5. The reaction product, (o-(NMe2)Ph-QA)Pt(1,2-η2-
6-σ-cycloocta-1,4-dienyl) (10a), features ligand 3 as a bidentate
rather than tridentate anionic amido ligand, the dimethylamino
group being unbound (Scheme 4). The originally neutral
cyclooctadiene donor ligand has been transformed to a formally
deprotonated anionic ligand that occupies the other two sites
of the pseudo-square-planar platinum center. Curiously, the
cyclic organic ligand does not bind to the platinum center as a
simple η3 π-allyl ligand. Rather, it binds in an unusual fashion
best described as a 1,2-η2-6-σ-cycloocta-1,4-dienyl ligand. The
X-ray structure of 10a shows the dimethylamino group project-
ing toward the side opposite the unbound double bond between
carbons C19 and C20 of the asymmetric cyclic ring ligand. We
infer that a distinct chemical isomer should exist whereby the
dimethylamino group projects into the opposite face, and
1
presume this to be the reason two isomers are observed by H
NMR spectroscopy on a uniform sample of the isolated batch
crystals. This isomer is sketched as 10b in Scheme 4. Hoping
to corroborate this assignment with an X-ray diffraction study,
(28) Although disordered, the X-ray data for 10b show that the geometry
around platinum places the amido N-donor trans to the dative bond
of the cyclic ring, as is the case for 10a (see Supporting Information).

Amido Complexes of Pt, Pd, and Ni
Inorganic Chemistry, Vol. 40, No. 20, 2001 5091
Scheme 5
Consistent with this scenario is the following observation: when
(COD)PtCl2 reacts with the lithium amide salt of 3, formed by
in situ deprotonation of 3 by nBuLi, the product yield of 10a,b
is significantly lower and the major byproduct of the reaction
is the free acid of ligand 3. The lithium amide has two competing
pathways, one in which it coordinates the platinum center and
one in which it acts as the base that deprotonates the cyclic
diene ring.
IV. Conclusions
The preparative groundwork for a series of related ligands
based upon an 8-quinolinylamine motif has been established.
Palladium-catalyzed cross-coupling methods proved very useful
for the preparation of 1 and the related amines 2-4, all of which
present promising ligands for transition metal chemistry.
Establishing the coordination chemistry of these ligands is a
necessary first step in their development, and this introductory
manuscript illustrates our initial progress into their group 10
chemistry. In contrast to the straightforward tridentate binding
of 1 to divalent platinum, we have elucidated a striking dif-
ference for ligands 2-4. These ligands react with (COD)PtCl2
to afford unusual examples of coordinated cyclic dienes derived
from the COD-containing starting material. We will report on
the potential of the systems developed herein for stoichiometric
and catalytic transformations in due course.
An explanation for the formation of products 10 and 11
remains to be put forward. While we are unaware of similar
(1,2-η2-6-σ-cycloocta-1,4-dienyl) ligands in group 10 chemistry,
the literature does provide one precedent for such a ligand.
Kubiak and co-workers established that the addition of relatively
soft bases to the cationic iridium complex [Ir(triphos)(η4-1,5-
cylcooctadiene)][Cl] effected deprotonation of the cyclic ring
and formation of a structurally characterized iridium(I) product,
Ir(triphos)(1,2-η2-6-σ-cycloocta-1,4-dienyl).29 Scheme 5 pos-
tulates a related scenario for the formation of complex 11 (and
by analogy complexes 10a and 10b). Ligand 4 coordinates the
divalent platinum starting material with concomitant loss of HCl.
This results in an unobserved cationic species susceptible to
deprotonation by triethylamine base at the C24 position of the
cyclic diene ring of 10 (or the related C20 position of 11).
Acknowledgment. We wish to thank the California Institute
of Technology and the Dreyfus Foundation for their generous
support of this research through a start-up grant and a Dreyfus
Foundation New Faculty Award.
Supporting Information Available: Full details for X-ray struc-
tures of compounds 5-11, including tables of positional parameters,
displacement parameters, and bond lengths and angles. This material
is available free of charge via the Internet at http://pubs.acs.org.
(29) Gull, A. M.; Fanwick, P. E.; Kubiak, C. P. Organometallics 1993,
12, 2121.
IC010336P