Tris(4-methylpiperazin-1-yl)phosphane, P(NC4H 8NMe)3: Synthesis, structural studies, group 10 and 11 metal complexes and catalytic investigations

Article abstract of DOI:10.1002/ejic.200700900

Group 10 and 11 metal complexes of a multidentate phosphorus-nitrogen donor ligand tris(4-methylpiperazin-1-yl)-phosphane, P(NC₄H ₈NMe)₃ (1) are reported. The reactions of 1 with an equimolar amount of CuX (X = Cl, Br and I) afford tetranuclear cubane-like complexes [(CuX)-{P(NC₄H₈NMe)₃}]₄ (2, X = Cl; 3, X = Br and 4, X = I) in excellent yield. Treatment of 1 with AuCl(SMe₂) produces a mononuclear complex, [(AuCl){P(NC ₄H₈NMe)₃}] (5). Reaction of 1 with AgCN produces a 2D Ag^I polymeric sheet, [(AgCN)2-{P(NC₄H ₈NMe)₃}]_n (6) in moderate yield. The similar 1:1 reactions of 1 with AgX (X = Cl and Br) furnish dinuclear complexes, [(AgX){P(NC₄H₈NMe)₃}]₂ (7, X = Cl and 8, X = Br). The 2:1 reactions of 1 with [M(COD)Cl₂] (M = Pd or Pt) afford [{P(NC₄H₈NMe)₃}₂MCl ₂] (9, M = Pd and 10, M = Pt) in quantitative yield. The molecular structures of complexes 1-3 and 6 are established through single-crystal X-ray diffraction studies. The catalytic activity of the Pd^II complex 9 has been investigated in Suzuki cross coupling reactions. Wiley-VCH Verlag GmbH & Co. KGaA, 2008.

Full text of DOI:10.1002/ejic.200700900

FULL PAPER
DOI: 10.1002/ejic.200700900
Tris(4-methylpiperazin-1-yl)phosphane, P(NC4H8NMe)3: Synthesis, Structural
Studies, Group 10 and 11 Metal Complexes and Catalytic Investigations
Chelladurai Ganesamoorthy,[a] Joel T. Mague,[b] and Maravanji S. Balakrishna*[a]
Keywords: Phosphanes / Group 10 and 11 metal complexes / Cubane-like structure / Homogeneous catalysis / C–C coupling
Group 10 and 11 metal complexes of a multidentate phos-
phorus–nitrogen donor ligand tris(4-methylpiperazin-1-yl)-
phosphane, P(NC4H8NMe)3 (1) are reported. The reactions
of 1 with an equimolar amount of CuX (X = Cl, Br and I)
afford tetranuclear cubane-like complexes [(CuX)-
{P(NC4H8NMe)3}]4 (2, X = Cl; 3, X = Br and 4, X = I) in excel-
actions of 1 with AgX (X = Cl and Br) furnish dinuclear com-
plexes, [(AgX){P(NC4H8NMe)3}]2 (7, X = Cl and 8, X = Br).
The 2:1 reactions of 1 with [M(COD)Cl2] (M = Pd or Pt) afford
[{P(NC4H8NMe)3}2MCl2] (9, M = Pd and 10, M = Pt) in quan-
titative yield. The molecular structures of complexes 1–3 and
6 are established through single-crystal X-ray diffraction
lent yield. Treatment of 1 with AuCl(SMe2) produces a mono- studies. The catalytic activity of the PdII complex 9 has been
nuclear complex, [(AuCl){P(NC4H8NMe)3}] (5). Reaction of 1
with AgCN produces a 2D AgI polymeric sheet, [(AgCN)2-
investigated in Suzuki cross coupling reactions.
(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim,
{P(NC4H8NMe)3}]n (6) in moderate yield. The similar 1:1 re- Germany, 2008)
donor functionalities, which may produce more coordina-
Introduction
tive interactions to give interesting structures with extended
networks. As a part of our interest in designing new ligands
and studying their coordination behavior and catalytic ap-
plications,[10] we report herein the synthesis, coordination
chemistry and catalytic investigations of tris(4-methylpiper-
azin-1-yl)phosphane, P(NC4H8NMe)3 (1).
In recent years there has been a growing interest in the
synthesis of complex structures including polymers, 2D
sheets, helices and cage complexes through the use of dy-
namic coordination chemistry[1] and weak intermolecular
forces such as hydrogen bonding, π-stacking, dipole-dipole
attractions and van der Waals interactions.[2] The motiva-
tion behind such investigations is to produce molecules with
intriguing architectures and topologies, and with properties
for producing functional solid materials for catalysis and
optical and magnetic applications.[3] Multidentate ligands
containing both hard and soft donor atoms with Group 11
metal derivatives have been used widely in this field.[4]
Other than the coordinative interaction afforded by these
multidentate ligands, the metals often show weak bonding
interactions between the closed-shell metal centers to pro-
duce novel molecular architectures with exciting optical
properties.[5] The nature of this d10/d10 interaction has been
of particular interest to theoreticians and spectroscopists
for a long time.[6] The nature of the product formed de-
pends on the arrangement of rhombic M2X2 units that can
be not only simple dimers,[7] but also cubane-like[8] or step
structures.[9] It would be interesting to study interactions of
Group 11 halides with phosphanes containing additional
Results and Discussion
The reaction of phosphorus trichloride with six equiva-
lents of N-methylpiperazine afforded a mixed donor multi-
dentate
ligand
tris(4-methylpiperazin-1-yl)phosphane,
P(NC4H8NMe)3 (1) in good yield.[11] Compound 1 is a
white crystalline solid that readily absorbs moisture from
the atmosphere to become deliquescent. The crude product
can be purified easily by dissolving it in petroleum ether
and filtering to remove impurities. Treatment of 1 with CuX
(X = Cl, Br and I) in an equimolar ratios produces tetranu-
clear complexes, [(CuX){P(NC4H8NMe)3}]4 (2, X = Cl; 3,
X = Br; 4, X = I) in quantitative yields, as shown in
Scheme 1. Complexes 2 and 3 are pale green solids, whereas
complex 4 is a white crystalline solid. A similar reaction
with AuCl(SMe2) in a 1:1 molar ratio afforded a mono-
nuclear complex, [(AuCl){P(NC4H8NMe)3}] (5). The 31P
NMR spectra of complexes 2–5 show single resonances at
98.9, 92.7, 79.5 and 102.3 ppm, respectively, which are shi-
elded compared to the free ligand 1 (δ = 112.2 ppm). In the
1H NMR spectra of complexes 2–5, the peak corresponding
to the N-methyl protons appears as a singlet in the region
2.24–2.30 ppm, whereas the –NMeCH2 and –NCH2 pro-
[a] Phosphorus Laboratory, Department of Chemistry, Indian In-
stitute of Technology,
Bombay, Mumbai 400076, India
Fax: +91-22-2572-3480
E-mail: krishna@chem.iitb.ac.in
[b] Department of Chemistry, Tulane University,
New Orleans, Louisiana 70118, USA
596
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Studies on a Mixed Donor Multidentate Phosphane Ligand
Scheme 1.
tons appear as broad singlets in the regions 2.33–2.36 and Table 1. NMR spectroscopic data for compounds 1–10.
3.10–3.17 ppm, respectively. The spectral and analytical
data support the proposal that 2–5 form only monoligated
complexes, and the structures of 1–3 were confirmed by sin-
gle crystal X-ray diffraction studies.
31P NMR
(δ, ppm)
1JXP / Hz
1H NMR (δ, ppm)
(X = Ag or Pt) –NMe MeNCH2– –NCH2–
1
2
3
4
5
6
7
8
9
112.2 (s)
98.9 (s)
2.27 (s) 2.32 (br. s) 2.94 (br. s)
2.27 (s) 2.36 (br. s) 3.10 (br. s)
2.25 (s) 2.35 (br. s) 3.12 (br. s)
2.24 (s) 2.33 (br. s) 3.17 (br. s)
2.22 (s) 2.30 (br. s) 3.15 (br. s)
2.30 (s) 2.37 (br. s) 3.03 (br. s)
2.29 (s) 2.38 (br. s) 3.09 (br. s)
2.25 (s) 2.35 (br. s) 3.09 (br. s)
2.23 (s) 2.37 (br. s) 3.22 (br. s)
2.28 (s) 2.41 (br. s) 3.27 (br. s)
The reaction of 1 with AgCN is not dependent on the
stoichiometry of the reagents or the reaction conditions,
and affords a 2D zigzag polymeric sheet, [(AgCN)2-
{P(NC4H8NMe)3}]n (6) in moderate yield. The equimolar
reactions of 1 with AgX (X = Cl or Br) afford halo-bridged
dinuclear complexes, [(AgX){P(NC4H8NMe)3}]2 (7, X =
Cl; 8, X = Br) in good yield. The 31P NMR spectrum of
complex 6 shows a broad doublet centered at δ = 108.8 ppm
92.7 (br. s)
79.5 (br. s)
102.3 (s)
108.8 (d)
111.4 (2 d)
108.7 (2 d)
89.5 (s)
717
929, 804
854, 743
10 84.4 (s)
3236
1
with a JAgP coupling of 717 Hz, whereas complexes 7 and
8 show two doublets centered at δ = 111.4 and 108.7 ppm,
respectively, with 1J109
and 1J107
couplings of 929
The Crystal and Molecular Structures of 1–3 and 6
AgP
AgP
1
and 804 Hz and of 854 and 743 Hz, respectively. The JAgP
values for complexes 6–8 follow the order ClϾBrϾCN,
which was also observed for (tBu)3PAgX (X = Cl, Br,
CN)[12] and [Cy3PAgX]2 (X = Cl, Br).[13] The 2:1 reactions
Views of the molecular structures of compounds 1–3 and
6 with atom numbering schemes are shown in Figures 1, 2,
of
1 with [M(COD)Cl2] (M = Pd or Pt) afford
[{P(NC4H8NMe)3}2MCl2] (9, M = Pd; 10, M = Pt) in
quantitative yield. The 31P NMR spectra of complexes 9
and 10 consist of single resonances at δ = 89.5 and
84.4 ppm, respectively, in which the platinum bound phos-
1
phorus center of 10 exhibits 195Pt satellites with a JPt–P
1
coupling of 3236 Hz. The H NMR spectroscopic data for
complexes 6–10 are consistent with the proposed structures
(Table 1). The IR spectrum of complex 6 shows a strong
ν(CN) band at 2140 cm–1, which is at a slightly lower fre-
quency when compared to the same band in the spectrum
of free AgCN [ν(CN) = 2164 cm–1].[14] The spectral and an-
alytical data support the proposed structures for complexes
6–10, and the structure of complex 6 was confirmed by a
single crystal X-ray diffraction study.
Figure 1. Molecular structure of 1. All hydrogen atoms have been
omitted for clarity. Displacement ellipsoids are drawn at the 50%
probability level.
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597

C. Ganesamoorthy, J. T. Mague, M. S. Balakrishna
FULL PAPER
and 3. Crystal data and details of the structure determi- units in an alternating zigzag fashion to form an AgI poly-
nations are given in Table 5, while selected bond lengths meric chain. These chains are stacked one over the other,
and bond angles are given in Tables 2 and 3.
with a weak nitrogen coordinative interaction between the
N-methylpiperazine moiety and Ag2 [Ag2–N6, 2.605(2) Å],
to yield a 2D AgI sheet. The Ag···N interactions observed
are nontrivial and are 0.03 Å shorter than those found in
the AgC(CN)3 based coordination polymer Ag(tcm)(bpe)
[tcm = tricyanomethanide, bpe = 1,2-bis(4-pyridyl)eth-
ane].[1d] In 6, Ag1 has trigonal planar geometry being
bonded to the nitrogen atoms of two linear [NCAgCN]–
bridges and a phosphorus atom of 1. The angles about Ag1,
P–Ag1–N7, P–Ag1–N8 and N7–Ag1–N8, are 126.15(5),
133.31(6) and 100.48(8)°, respectively, with the sum of these
angles being close to 360°. The Ag2 center adopts a T-shape
coordination geometry that consists of the carbon atoms of
the two bridging cyanide groups and a nitrogen atom of the
N-methylpiperazine group, with the C16–Ag2–C17, N6–
Ag2–C16, N6–Ag2–C17 angles being 160.53(9), 104.96(8)
and 94.24(7)°, respectively. The Ag1–P, Ag1–N7 and Ag1–
N8 bond lengths are 2.355(1), 2.233(2) and 2.173(2) Å,
respectively. These values are significantly shorter than the
corresponding values found for the analogous 1D polymers
of P(Cy)3[14], and the functionalized cyclodiphosphazane
cis-{(o-MeOC6H4O)P(µ-NtBu)}2.[17] The Ag2–C16 and
Ag2–C17 bond lengths are 2.068(2) and 2.079(2) Å, respec-
tively, and are 0.03 Å longer than the corresponding dis-
tances observed in the above mentioned polymers.
Figure 2. Molecular structure of 2. All hydrogen atoms have been
omitted for clarity. Displacement ellipsoids are drawn at the 50%
probability level.
The molecule 1 crystallizes in the triclinic crystal system
¯
with space group P1 (No.2). There are two short, P1–N3
and P1–N5, and one long, P1–N1, phosphorus–nitrogen
bonds with distances of 1.693(1), 1.691(2) and 1.741(2) Å,
respectively. The N-methylpiperazine groups, which are
Suzuki–Miyaura Cross-Coupling Reactions
The palladium catalyzed Suzuki cross-coupling reaction
linked through short bonds to the phosphorus atom, are is one of the efficient methods for forming symmetric and
twisted in opposite directions, this was also observed in nonsymmetric biaryl compounds in organic synthesis.[18]
analogous tertiary aminophosphanes.[15] The N1–P1–N3 Complex 9 proved to be an efficient catalyst for the Suzuki–
and N1–P1–N5 angles [97.29(7)° and 97.18(7)°] are smaller Miyaura cross-coupling reactions of aryl bromides with
than the N3–P1–N5 angle [110.56(7)°], and the sum of the phenylboronic acid, and led to good conversions with low
angles around phosphorus atom is 305.03°.
catalytic loadings. The Suzuki–Miyaura cross-coupling re-
The molecular structure of 2 consists of a distorted cub- actions were carried out in methanol (5 mL) with potassium
ane-like P4Cu4Cl4 framework, with alternating corners of carbonate as base. For example, bromo- or iodobenzene
the cube being occupied by copper and chlorine atoms, and and phenylboronic acid in the presence of K2CO3 in meth-
with each phosphorus atom projecting radially from a cop- anol gives 95% conversion within 4–5 h, at room tempera-
per atom. The Cu–P bond lengths are equal within experi- ture with 0.05 mol-% of catalyst (Table 4, entries 1 and 2).
mental error with an average of 2.174(1) Å, which is com- Higher conversion rates were realized when activated aryl
parable to the distance found in the PEt3 analog bromides were used as substrates (Table 4, entries 3, 5 and
[2.176(1) Å].[8a] The Cu–Cl bond lengths vary from 2.321(1) 8). The coupling of 4-bromoacetophenone with phenylbo-
to 2.602(1) Å. The six Cu···Cu bond lengths, in increasing ronic acid afforded 75% of the coupled product within half
order, are 3.092, 3.238, 3.323, 3.354, 3.377 and 3.384 Å, an hour (turn over frequency: 3000) and complete conver-
which are longer than those found in the Cu4Cl4 cube that sion was achieved after 4 h at room temperature. Even
has bridged-bidentate phosphaalkene ligands (3.058– though good conversion was observed with deactivated 4-
3.218 Å).[16] The Cl–Cu–Cl angles range from 88.74(2) to bromoanisole (Table 4, entry 4) very low catalytic conver-
101.09(2)°, whereas the Cu–Cl–Cu angles are smaller and sion was observed with 1-bromo-2,4-dimethoxybenzene
range from 78.05(2) to 89.05(2)°.
(Table 4, entry 11). The coupling reactions of bulky aryl
Complex 3 is isomorphous and isostructural with 2 and bromides with phenylboronic acid tend to give moderate
has a similar P4Cu4Br4 cubane core. The bond lengths and yield at room temperature (Table 4, entry 9), however the
bond angles in 3 are similar to those in 2.
The molecular structure of
conversion rate and yield can be improved by carrying out
6
consists of the reaction under reflux conditions (Table 4, entry 10).
[{P(NC4H8NMe)3}Ag]+ moieties bridged by [NCAgCN]– Coupling reactions performed with 1,3-dibromobenzene
598
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Studies on a Mixed Donor Multidentate Phosphane Ligand
Figure 3. (top) A portion of the zigzag chain present in the structure of 6. Symmetry operations: (i) –1 + x, y, 1 + z; (ii) 0.5 – x, 0.5 +
y, 0.5 – z; (iii) 0.5 – x, 0.5 + y, –0.5 – z; (iv) –1 + x, –1 + y, 1 + z. (bottom) A portion of the 2-D sheet present in the structure of 6. All
hydrogen atoms have been omitted for clarity, and displacement ellipsoids are drawn at the 50% probability level in both diagrams.
yielded 83% of 1,1Ј:3Ј,1"-terphenyl and 17% of 3-bromobi- unreacted 1,4-dibromobenzene (2%) remained. All the 1,4-
phenyl after 2 h with the complete consumption of the 1,3- dibromobenzene was consumed within 5 h and a conversion
dibromobenzene reagent. A gradual increase in the yield of of Ͻ97% of 1,1Ј:4Ј,1ЈЈ-terphenyl was achieved within 24 h
1,1Ј:3Ј,1"-terphenyl was observed with time and a maxi- (Table 4, entry 14). Similarly, the coupling reactions per-
mum of 98% conversion to 1,1Ј:3Ј,1ЈЈ-terphenyl was formed with 9, 10-dibromoanthracene and 1, 3, 5-tribromo-
achieved after 24 h (Table 4, entry 13). Similarly 1,4-dibro- benzene with phenylboronic acid yielded 100% of di- and
mobenzene yielded 86% of 1,1Ј:4Ј,1ЈЈ-terphenyl and 12% tri-substituted derivatives, respectively (Table 4, entries 15
of 4-bromobiphenyl after 3 h however, a small amount of and 16), whereas 4,4Ј-dibromobiphenyl afforded 83% of di-
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599

C. Ganesamoorthy, J. T. Mague, M. S. Balakrishna
FULL PAPER
Table 2. Selected bond lengths and bond angles for compounds 1 and 2.
Compound 1
Bond lengths / Å
Compound 2
Bond lengths / Å
Bond angles / °
Bond angles / °
P1–N1
P1–N3
P1–N5
N1–C1
N1–C4
N3–C6
N3–C9
N5–C11
N5–C14
1.741(2)
N1–P1–N3
N1–P1–N5
N3–P1–N5
P1–N1–C1
P1–N1–C4
P1–N3–C6
P1–N3–C9
P1–N5–C11
P1–N5–C14
97.29(7)
97.18(7)
Cu1–P1
Cu2–P2
Cu3–P3
Cu4–P4
Cu1–Cl1
Cu1–Cl2
Cu1–Cl4
Cu2–Cl1
Cu2–Cl2
Cu2–Cl3
Cu3–Cl2
Cu3–Cl3
Cu3–Cl4
Cu4–Cl1
Cu4–Cl3
Cu4–Cl4
2.1739(5)
2.1740(6)
2.1756(5)
2.1732(6)
2.4882(6)
2.3978(6)
2.3701(6)
2.3212(6)
2.4919(6)
2.5234(6)
2.3860(6)
2.3425(6)
2.6020(6)
2.4215(6)
2.4874(6)
2.3668(6)
Cl1–Cu1–Cl2
Cl1–Cu1–Cl4
Cl2–Cu1–Cl4
Cl1–Cu2–Cl2
Cl1–Cu2–Cl3
Cl2–Cu2–Cl3
Cl2–Cu3–Cl3
Cl2–Cu3–Cl4
Cl3–Cu3–Cl4
Cl1–Cu4–Cl3
Cl1–Cu4–Cl4
Cl3–Cu4–Cl4
Cl1–Cu1–P1
Cl1–Cu2–P2
Cl2–Cu3–P3
Cl1–Cu4–P4
92.40(2)
99.08(2)
95.55(2)
94.18(2)
97.23(2)
88.74(2)
95.75(2)
90.02(2)
94.20(2)
95.62(2)
101.09(2)
96.64(2)
109.08(2)
130.82(2)
130.23(2)
113.70(2)
1.693(1)
1.691(2)
1.476(2)
1.470(2)
1.456(2)
1.464(2)
1.463(2)
1.461(2)
110.56(7)
114.66(1)
114.38(1)
118.61(1)
125.07(1)
126.40(1)
117.10(1)
Table 3. Selected bond lengths and bond angles for compounds 3 and 6.
Compound 3
Bond lengths / Å
Compound 6
Bond lengths / Å
Bond angles / °
Bond angles / °
Cu1–P1
Cu2–P2
Cu3–P3
Cu4–P4
Br1–Cu1
Br1–Cu2
Br1–Cu3
Br2–Cu2
Br2–Cu3
Br2–Cu4
Br3–Cu1
Br3–Cu3
Br3–Cu4
Br4–Cu1
Br4–Cu2
Br4–Cu4
2.1886(6)
2.1918(6)
2.1880(5)
2.1939(6)
2.5889(4)
2.5392(4)
2.4946(4)
2.4849(4)
2.7184(4)
2.5013(4)
2.6036(4)
2.4697(4)
2.6053(4)
2.4537(4)
2.6029(4)
2.5302(4)
Br1–Cu1–Br3
Br1–Cu1–Br4
Br3–Cu1–Br4
Br1–Cu2–Br2
Br1–Cu2–Br4
Br2–Cu2–Br4
Br1–Cu3–Br2
Br1–Cu3–Br3
Br2–Cu3–Br3
Br2–Cu4–Br3
Br2–Cu4–Br4
Br3–Cu4–Br4
Br1–Cu1–P1
Br1–Cu2–P2
Br1–Cu3–P3
Br2–Cu4–P4
93.70(1)
96.26(1)
101.42(1)
97.25(1)
93.85(1)
103.26(1)
92.55(1)
99.47(1)
97.24(1)
99.44(1)
104.91(1)
99.34(1)
121.51(2)
120.73(2)
128.38(2)
125.48(2)
Ag1–P
2.355(1)
2.233(2)
P–Ag1–N7
P–Ag1–N8
N7–Ag1–N8
N6–Ag2–C16
C16–Ag2–C17
N6–Ag2–C17
Ag1–P–N1
Ag1–P–N3
Ag1–P–N5
N1–P–N3
126.15(5)
133.31(6)
100.48(8)
104.96(8)
160.53(9)
94.24(7)
113.34(7)
116.85(6)
111.87(6)
100.87(9)
Ag1–N7
Ag1–N8
Ag2–N6
Ag2–C16
Ag2–C17
P–N1
P–N3
P–N5
N7–C17
N8–C16
2.173(2)
2.605(2)
2.068(2)
2.079(2)
1.654(2)
1.700(2)
1.672(2)
1.146(3)
1.143(3)
Table 4. Details of Suzuki cross-coupling reactions for aryl bromides with phenylboronic acid catalyzed by [{P(NC4H8NMe)3}2PdCl2] (9).
Entry
Aryl bromide
Condition[a]
% Conversion[b]
TOF[c]
TON[d]
1
2
3
4
5
6
7
8
bromobenzene
iodobenzene
0.05 mol-%, room temp., 4 h
0.05 mol-%, room temp., 5 h
0.05 mol-%, room temp., 1 h
0.05 mol-%, room temp., 6 h
0.05 mol-%, room temp., 4 h
0.05 mol-%, room temp., 12 h
0.05 mol-%, reflux, 4 h
95
96
Ͼ99
99
81
55
99
97
64
97
32
35
100
100
100
100
83
475
384
1980
330
405
92
495
485
53
647
320
117
1000
400
250
42
1900
1920
1980
1980
1620
1100
1980
1940
1280
1940
640
4-bromoacetophenone
4-bromoanisole
4-bromobenzaldehyde
3-bromobenzaldehyde
3-bromobenzaldehyde
4-bromobenzonitrile
2-bromo-6-methoxynaphthalene 0.05 mol-%, room temp., 24 h
2-bromo-6-methoxynaphthalene 0.05 mol-%, reflux, 3 h
1-bromo-2,4-dimethoxybenzene
2-bromopyridine
1,3-dibromobenzene
1,4-dibromobenzene
9,10-dibromoanthracene
1,3,5-tribromobenzene
4,4Ј-dibromobiphenyl
0.05 mol-%, room temp., 4 h
9
10
11
12
13
14
15
16
17
0.05 mol-%, reflux, 2 h
0.05 mol-%, room temp., 6 h
0.05 mol-%, room temp., 2 h
0.05 mol-%, room temp., 5 h
0.1 mol-%, room temp., 4 h
0.1 mol-%, room temp., 24 h
0.1 mol-%, room temp., 24 h
700
2000
2000
1000
1000
830
35
[a] Aryl halide (0.5 mmol), phenylboronic acid (0.75, 1.25 and 1.75 mmol for mono-, di- and tribromo derivatives, respectively), K2CO3
(1 mmol), MeOH (5 mL). [b] Percentage conversion to coupled product as determined by GC, based on aryl halides, and averaged over
two runs. [c] Defined as mole product per mole of catalyst per hour. [d] Defined as mole product per mole of catalyst.
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Eur. J. Inorg. Chem. 2008, 596–604

Studies on a Mixed Donor Multidentate Phosphane Ligand
corded on a Nicolet Impact 400 FTIR instrument as KBr disks.
The microanalyses were performed using a Carlo–Erba Model 1112
elemental analyzer. The melting points were observed in capillary
tubes and are uncorrected. GC analyses were performed on a Per-
kin–Elmer Clarus 500 GC fitted with a packed column.
substituted derivative after 24 h (Table 4, entry 17). In con-
trast, the coupling reaction of 2-bromopyridine with phen-
ylboronic acid was less successful and gave only moderate
conversion (35%) after 6 h at room temperature (Table 4,
entry 12). In most cases there was not much improvement
in the conversions after a set period of time, which may be
due to the deactivation of the catalyst (Table 4, entries 5, 6,
9, 11, 12 and 17).
The Suzuki cross-coupling reaction is strongly influenced
by the solvent and base present in the reaction mixture. For
example, replacing K2CO3 with Cs2CO3 or K3PO4 and em-
ploying non-polar solvents such as toluene and n-hexane
gave low catalytic conversion rates. The homogeneous na-
ture of the catalysis was checked by the classical mercury
test.[19] Addition of a drop of mercury to the reaction mix-
ture did not affect the conversion level of the reaction,
which suggests that the catalysis is homogeneous in nature
since heterogeneous catalysts would form an amalgam, and
therefore be poisoned by the mercury.
Synthesis of P(NC4H8NMe)3 (1): A solution of N-methylpiperazine
(20.7 g, 0.206 mol) in petroleum ether (20 mL; boiling range 60–
80 °C) was added drop wise to a solution of phosphorus trichloride
(4.72 g, 0.034 mol) also in petroleum ether (100 mL) at 0 °C with
constant stirring. The reaction mixture was slowly warmed to room
temperature, allowed to stir overnight, and then filtered through
celite. The filtrate was concentrated under vacuum and stored at
–30 °C for two days to give an analytically pure white crystals of
1. Yield 80% (9.04 g); m.p. 78–80 °C. C15H33N6P (328.4): calcd. C
54.85, H 10.13, N 25.59; found C 54.82, H 10.10, N 25.51. 1H
NMR (400 MHz, CDCl3): δ = 2.27 (s, 9 H, NCH3), 2.32 (br. s, 12
H, CH2), 2.94 ppm (br. s, 12 H, CH2). 31P{1H} NMR (162 MHz,
CDCl3): δ = 112.2 ppm (s).
Synthesis of [(CuCl){P(NC4H8NMe)3}]4 (2): A solution of cuprous
chloride (0.059 g, 0.597 mmol) in acetonitrile (5 mL) was added
drop wise to a solution of 1 (0.196 g, 0.597 mmol) also in acetoni-
trile (7 mL) with constant stirring. After stirring for 4 h, the solu-
tion was concentrated to 5 mL under vacuum and stored at room
temperature overnight to give analytically pure pale green
crystals of 2. Yield 82% (0.209 g); m.p. 148–150 °C (dec.).
C60H132Cl4Cu4N24P4 (1709.7): calcd. C 42.15, H 7.78, N 19.66;
Conclusions
The tertiary phosphane ligand 1 readily reacts with vari-
ous Group 11 metal derivatives to give either tetranuclear
clusters or a 2D polymeric sheet depending upon the reac-
tion conditions and the stoichiometry of the reactants. With
copper(I) halides, tetranuclear cubane complexes 2–4 were
formed, whereas with AgCN a 2D polymeric sheet, involv-
ing week Ag–N (NMe nitrogen atom of MeNC4H8N-) in-
teractions, was isolated. Similar reactions of 1 with AuCl-
(SMe2) and silver(I) halides afforded mono- and dinuclear
complexes 5 and 7–8, respectively. Surprisingly, the ligand
did not show multidentate behavior despite the presence of
three terminal nitrogen atoms. The PdII complex 9 effec-
tively catalyzes the Suzuki cross-coupling reactions of sev-
eral aryl mono-, di-, and tri-bromides with phenylboronic
acid at room temperature. Further reactions of ligand 1
with Group 10 metals and their catalytic utility in various
other organic transformations are under active investigation
in our laboratory.
1
found C 42.19, H 7.75, N 19.64. H NMR (400 MHz, CDCl3): δ =
2.27 (s, 36 H, NCH3), 2.36 (br. s, 48 H, CH2), 3.10 ppm (br. s, 48
H, CH2). 31P{1H} NMR (162 MHz, CDCl3): δ = 98.9 ppm (s).
Synthesis of [(CuBr){P(NC4H8NMe)3}]4 (3): Compound 3 was syn-
thesized by a procedure similar to that for 2 using cuprous bromide
(0.052 g, 0.360 mmol) and 1 (0.118 g, 0.360 mmol). Yield 88%
(0.149 g); m.p. 210–214 °C (dec.). C60H132Br4Cu4N24P4 (1887.5):
calcd. C 38.18, H 7.05, N 17.81; found C 38.11, H 7.08, N 17.78.
1H NMR (400 MHz, CDCl3): δ = 2.25 (s, 36 H, NCH3), 2.35 (br.
s, 48 H, CH2), 3.12 ppm (br. s, 48 H, CH2). 31P{1H} NMR
(121 MHz, CDCl3): δ = 92.7 ppm (br. s).
Synthesis of [(CuI){P(NC4H8NMe)3}4] (4): Compound 4 was syn-
thesized by a procedure similar to that for 2 using cuprous iodide
(0.068 g, 0.357 mmol) and 1 (0.117 g, 0.357 mmol). Yield 95%
(0.176 g); m.p. 150–152 °C (dec.). C60H132Cu4I4N24P4 (2075.5):
calcd. C 34.72, H 6.41, N 16.20; found C 34.78, H 6.44, N 16.26.
1H NMR (400 MHz, CDCl3): δ = 2.24 (s, 36 H, NCH3), 2.33 (br.
s, 48 H, CH2), 3.17 ppm (br. s, 48 H, CH2). 31P{1H} NMR
(162 MHz, CDCl3): δ = 79.5 ppm (br. s).
Experimental Section
Synthesis of [(AuCl){P(NC4H8NMe)3}] (5): A CH2Cl2 (5 mL) solu-
tion of 1 (0.056 g, 0.169 mmol) was added drop wise to a solution
of AuCl(SMe2) (0.050 g, 0.169 mmol) also in CH2Cl2 (5 mL). The
reaction mixture was stirred at room temperature for 4 h. The re-
sulting solution was concentrated to 3 mL, layered with 3 mL of
petroleum ether, and kept at –30 °C for one day to give 5 as an
analytically pure white crystalline solid. Yield 79% (0.075 g); m.p.
156–158 °C (dec.). C15H33AuClN6P (560.8): calcd. C 32.12, H 5.93,
N 14.98; found C 32.16, H 5.90, N 15.01. 1H NMR (400 MHz,
CDCl3): δ = 2.22 (s, 9 H, NCH3), 2.30 (br. s, 12 H, CH2), 3.15 ppm
(br. s, 12 H, CH2). 31P{1H} NMR (121 MHz, CDCl3): δ =
102.3 ppm (s).
Reagents and Techniques: All experimental manipulations were per-
formed under rigorous anaerobic conditions using Schlenk tech-
niques. All the solvents were purified by conventional procedures
and distilled prior to use. The gold(I) and silver(I) complexes 5–8,
were prepared under dark conditions by wrapping the reaction ves-
sel with aluminum foil. The metal precursors CuX (X = Cl and
Br),[20] AuCl(SMe2),[21] and [M(COD)Cl2] (M = Pd and Pt),[22] were
prepared according to published procedures. AgX (X = Cl, Br and
CN) were obtained from commercial sources and used without fur-
ther purification. The 1H and 31P{1H} NMR spectra were recorded
using Varian VXR 300 or VXR 400 spectrometers operating at the
appropriate frequencies using TMS and 85% H3PO4 as internal
and external references, respectively. The spectra were recorded in
CDCl3 solutions with CDCl3 as an internal lock; in all cases posi-
tive shifts lie downfield of the standard. Infrared spectra were re-
Synthesis of [(AgCN)2{P(NC4H8NMe)3}]n (6): A THF (3 mL) solu-
tion of 1 (0.061 g, 0.187 mmol) was added drop wise, at room tem-
perature, to a suspension of AgCN (0.050 g, 0.373 mmol) also in
THF (5 mL). The reaction mixture was stirred at room temperature
Eur. J. Inorg. Chem. 2008, 596–604
© 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
601

C. Ganesamoorthy, J. T. Mague, M. S. Balakrishna
FULL PAPER
for 12 h and was then filtered through celite. The filtrate was con-
centrated and stored at room temperature for several days to give
analytically pure white crystals of 6. Yield 64% (0.071 g); m.p. 184–
to a solution of 1 (0.083 g, 0.252 mmol) also in CH2Cl2 (7 mL).
The reaction mixture was stirred at room temperature for 5 h to
give clear yellow solution. The solution was concentrated to 3 mL,
186 °C (dec.). C17H33Ag2N8P (596.2): calcd. C 34.25, H 5.58, N diluted with 3 mL of petroleum ether, and stored at –30 °C for 1
18.79; found C 34.26, H 5.60, N 18.81. 1H NMR (400 MHz, day to give an analytically pure yellow precipitate of 9. Yield 95%
CDCl3): δ = 2.30 (s, 9 H, NCH3), 2.37 (br. s, 12 H, CH2), 3.03 ppm
(0.099 g); m.p. 106–108 °C (dec.). C30H66Cl2N12P2Pd (834.2): calcd.
C 43.19, H 7.97, N 20.15; found C 43.12, H 7.89, N 20.10. 1H
NMR (400 MHz, CDCl3): δ = 2.23 (s, 18 H, NCH3), 2.37 (br. s,
24 H, CH2), 3.22 ppm (br. s, 24 H, CH2). 31P{1H} NMR
(162 MHz, CDCl3): δ = 89.5 ppm (s).
(br. s, 12 H, CH2). 31P{1H} NMR (121 MHz, CDCl3): δ =
1
108.8 ppm (d, JAgP = 717 Hz). FT-IR (KBr disc:): ν = 2140 cm–1
˜
(νCN).
Synthesis of [(AgCl){P(NC4H8NMe)3}]2 (7): A CH2Cl2 (3 mL) solu-
tion of 1 (0.115 g, 0.350 mmol) was added drop wise, at room tem-
perature, to a suspension of AgCl (0.050 g, 0.350 mmol) also in
CH2Cl2 (5 mL). The reaction mixture was stirred at room tempera-
ture for 24 h and was then filtered through celite. The filtrate was
concentrated to 3 mL followed by the addition of petroleum ether
(8 mL) to give a white precipitate of 7. Recrystallization from a 1:1
dichloromethane/petroleum ether mixture at –30 °C afforded 7 as
an analytically pure white crystalline substance. Yield 78%
(0.129 g); m.p. 138–140 °C (dec.). C30H66Ag2Cl2N12P2 (943.5):
calcd. C 38.19, H 7.05, N 17.81; found C 38.26, H 7.06, N 17.85.
1H NMR (400 MHz, CDCl3): δ = 2.29 (s, 18 H, NCH3), 2.38 (br.
s, 24 H, CH2), 3.09 ppm (br. s, 24 H, CH2). 31P{1H} NMR
Synthesis of [{P(NC4H8NMe)3}2PtCl2] (10): Compound 10 was
synthesized by a procedure similar to that for 9 using [Pt(COD)-
Cl2] (0.030 g, 0.080 mmol) and 1 (0.053 g, 0.160 mmol). Yield 87%
(0.064 g); m.p. 140–142 °C (dec.). C30H66Cl2N12P2Pt (922.8): calcd.
C 39.04, H 7.21, N 18.21; found C 39.10, H 7.25, N 18.28. 1H
NMR (400 MHz, CDCl3): δ = 2.28 (s, 18 H, NCH3), 2.41 (br. s,
24 H, CH2), 3.27 ppm (br. s, 24 H, CH2). 31P{1H} NMR
1
(162 MHz, CDCl3): δ = 84.4 ppm (s, JPtP = 3236 Hz).
General Procedure for the Suzuki Cross-Coupling Reactions of Aryl
Bromides with Phenylboronic Acid: In a two-necked round-bot-
tomed flask, under an atmosphere of nitrogen, were placed the ap-
propriate amounts of aryl bromide (0.5 mmol), phenylboronic acid
(0.75 mmol), K2CO3 (0.138 g, 1 mmol) and methanol (5 mL). After
stirring for 2 minutes, 0.05 mol-% of a freshly prepared stock solu-
tion of [{P(NC4H8NMe)3}2PdCl2] (9) in dichloromethane was
added. The mixture was stirred at room temperature, or refluxed
under an atmosphere of nitrogen, and the course of the reaction
was monitored by GC analysis. After completion of the reaction,
the solvent was removed under reduced pressure. The residual mix-
ture was diluted with H2O (10 mL) and extracted with Et2O or
toluene (2ϫ6 mL). The combined organic fractions were dried
(MgSO4), stripped of the solvent under vacuum, and the residue
redissolved in 5 mL of dichloromethane. An aliquot was taken with
a syringe and subjected to GC analysis. Yields were calculated with
respect to the aryl halides.
(162 MHz, CDCl3): δ = 111.4 ppm (2d, J109
= 929, J107
=
AgP
AgP
804 Hz).
Synthesis of [(AgBr){P(NC4H8NMe)3}]2 (8): Compound 8 was syn-
thesized by a procedure similar to that for 7 using silver bromide
(0.061 g, 0.323 mmol) and 1 (0.106 g, 0.323 mmol). Yield 69%
(0.115 g); m.p. 160–162 °C (dec.). C30H66Ag2Br2N12P2 (1032.4):
calcd. C 34.90, H 6.44, N 16.28; found C 34.96, H 6.47, N 16.25.
1H NMR (400 MHz, CDCl3): δ = 2.25 (s, 18 H, NCH3), 2.35 (br.
s, 24 H, CH2), 3.09 ppm (br. s, 24 H, CH2). 31P{1H} NMR
(162 MHz, CDCl3): δ = 108.7 ppm (2d, J109
= 854, J107
=
AgP
AgP
743 Hz).
Synthesis of [{P(NC4H8NMe)3}2PdCl2] (9): A CH2Cl2 (5 mL) solu-
tion of [Pd(COD)Cl2] (0.036 g, 0.126 mmol) was added drop wise
Table 5. Crystallographic Information for Compounds 1–3 and 6.
1
2
3
6
Empirical formula
Fw
Crystal system
Space group
a / Å
C15H33N6P
328.44
C60H132Cl4Cu4N24P4
1709.74
C60H132Br4Cu4N24P4
1887.58
C17H33Ag2N8P
596.22
triclinic
triclinic
triclinic
monoclinic
P21/n (no. 14)
10.939(1)
19.123(2)
11.686(1)
90
94.755(2)
90
2436.1(4)
4
¯
¯
¯
P1 (no. 2)
P1 (no. 2)
P1 (no. 2)
7.0087(8)
9.2380(1)
15.201(2)
102.591(2)
91.919(2)
102.180(1)
935.7(2)
2
12.784(1)
16.137(1)
22.238(2)
76.991 (1)
78.755 (1)
68.661(1)
4131.0(6)
2
12.828(1)
16.213(1)
22.338(2)
76.632(1)
78.554(1)
69.303(1)
4193.4(6)
2
b / Å
c / Å
o
α /
β /
γ /
o
o
V / Å3
Z
ρcalcd. / gcm–3
µ (Mo-Ka) / mm–1
F(000)
1.166
0.154
360
1.375
1.274
1808
1.495
3.033
1952
1.626
1.692
1200
Crystal size / mm
T / K
2θ range /
0.16ϫ0.18ϫ0.20
100
1.4–28.3
7978
4232
0.024
1.02
0.0466
0.1247
0.15ϫ0.15ϫ0.21
100
1.4–28.3
37158
19161
0.023
1.04
0.0345
0.0895
0.13ϫ0.15ϫ0.21
100
1.4–28.3
37679
19457
0.018
1.05
0.0279
0.0718
0.19ϫ0.20ϫ0.37
100
2.0–27.8
21123
5669
0.025
1.05
0.0242
0.0587
o
Total number of reflections
Independent reflections
Rint
GoF (F2)
[a]
R1
[b]
wR2
[a] R1 = Σ||Fo| – |Fc||/Σ|Fo|. [b] wR2 = {[Σw(Fo – Fc )/Σw(Fo2)2]}1/2 w = 1/[σ2(Fo2) + (xP)2] where P = (Fo + 2Fc )/3.
2
2
2
2
602
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Eur. J. Inorg. Chem. 2008, 596–604

Studies on a Mixed Donor Multidentate Phosphane Ligand
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X-ray Crystallography: A crystal of each of the compounds 1–3
and 6 suitable for X-ray crystal analysis were mounted in a Cry-
oloop with a drop of Paratone oil, and placed in the cold nitrogen
stream of the Kryoflex attachment of the Bruker APEX CCD
diffractometer. Full spheres of data were collected, under the con-
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per scan) at f = 0, 120 and 240°, or a combination of three sets of
400 scans in ω (0.5° per scan) at f = 0, 90 and 180° plus two sets
of 800 scans in f (0.45° per scan) at ω = –30 and 210°. The raw
data were reduced to F2 values using the SAINT+ software,[24] and
global refinements of unit cell parameters using 4284–7898 reflec-
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absorption corrections as well as corrections for any crystal deterio-
ration during the data collection (SADABS).[25] All the structures
were solved by direct methods and refined by full matrix least
squares procedures using the SHELXTL program package.[26] Hy-
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riding contributions with isotropic displacement parameters tied to
those of the attached non-hydrogen atoms. Pertinent crystallo-
graphic data and other experimental details are summarized in
Table 5.
[5]
[6]
[7]
[8]
CCDC-658839 (for 1), -658840 (for 2), -658841 (for 3) and -658842
(for 6) contain the supplementary crystallographic data for this
paper. These data can be obtained free of charge from the Cam-
bridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/
data_request/cif.
[9]
Acknowledgments
[10]
We are grateful to the Department of Science and Technology
(DST), New Delhi for funding. C. G. thanks the Council of Scien-
tific and Industrial Research (CSIR), New Delhi for a Senior Re-
search Fellowship (SRF). We also thank SAIF, Mumbai, Depart-
ment of Chemistry Instrumentation Facilities, Mumbai, for spec-
tral and analytical data, and the Louisiana Board of Regents
through grant LEQSF (2002-03)-ENH-TR-67 for purchase of the
CCD diffractometer and the Tulane University for support for the
X-ray laboratory.
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