Syntheses and characterization of mono and dinuclear complexes of platinum group metals bearing benzene-linked bis(pyrazolyl)methane ligands

Article abstract of DOI:10.1016/j.jorganchem.2010.02.005

Reaction of the benzene-linked bis(pyrazolyl)methane ligands, 1,4-bis{bis(pyrazolyl)-methyl}benzene (L1) and 1,4-bis{bis(3-methylpyrazolyl)methyl}benzene (L2), with pentamethylcyclopentadienyl rhodium and iridium complexes [(η⁵-C₅Me₅)M(μ-Cl)Cl]₂ (M = Rh and Ir) in the presence of NH₄PF₆ results under stoichiometric control in both, mono and dinuclear complexes, [(η⁵-C₅Me₅)RhCl(L)]⁺ {L = L1 (1); L2 (2)}, [(η⁵-C₅Me₅)IrCl(L)]⁺ {L = L1 (3); L2 (4)} and [{(η⁵-C₅Me₅)RhCl}₂(μ-L)]²⁺ {L = L1 (5); L2 (6)}, [{(η⁵-C₅Me₅)IrCl}₂(μ-L)]²⁺ {L = L1 (7); L2 (8)}. In contrast, reaction of arene ruthenium complexes [(η⁶-arene)Ru(μ-Cl)Cl]₂ (arene = C₆H₆, p-ⁱPrC₆H₄Me and C₆Me₆) with the same ligands (L1 or L2) gives only the dinuclear complexes [{(η⁶-C₆H₆)RuCl}₂(μ-L)]²⁺ {L = L1 (9); L2 (10)}, [{(η⁶-p-ⁱPrC₆H₄Me)RuCl}₂(μ-L)]²⁺ {L = L1 (11); L2 (12)} and [{(η⁶-C₆Me₆)RuCl}₂(μ-L)]²⁺ {L = L1 (13); L2 (14)}. All complexes were isolated as their hexafluorophosphate salts. The single-crystal X-ray crystal structure analyses of [7](PF₆)₂, [9](PF₆)₂ and [11](PF₆)₂ reveal a typical piano-stool geometry around the metal centers with six-membered metallo-cycle in which the 1,4-bis{bis(pyrazolyl)-methyl}benzene acts as a bis-bidentate chelating ligand.

Full text of DOI:10.1016/j.jorganchem.2010.02.005

Journal of Organometallic Chemistry 695 (2010) 1375–1382
Contents lists available at ScienceDirect
Journal of Organometallic Chemistry
journal homepage: www.elsevier.com/locate/jorganchem
Syntheses and characterization of mono and dinuclear complexes of platinum
group metals bearing benzene-linked bis(pyrazolyl)methane ligands
Kota Thirumala Prasad a, Bruno Therrein b, Kollipara Mohan Rao a,
*
a Department of Chemistry, North Eastern Hill University, Shillong 793 022, India
b Service Analytique Facultaire, University of Neuchatel, Case Postale 158, CH-2009, Neuchatel, Switzerland
a r t i c l e i n f o
a b s t r a c t
Article history:
Reaction of the benzene-linked bis(pyrazolyl)methane ligands, 1,4-bis{bis(pyrazolyl)-methyl}benzene
(L1) and 1,4-bis{bis(3-methylpyrazolyl)methyl}benzene (L2), with pentamethylcyclopentadienyl rho-
Received 15 December 2009
Received in revised form 3 February 2010
Accepted 5 February 2010
dium and iridium complexes [(
under stoichiometric control in both, mono and dinuclear complexes, [(
L2 (2)}, [(
5-C5Me5)IrCl(L)]+ {L = L1 (3); L2 (4)} and [{( 5-C5Me5)RhCl}2(
[{(
5-C5Me5)IrCl}2( -L)]2+ {L = L1 (7); L2 (8)}. In contrast, reaction of arene ruthenium complexes
[(
6Ùarene)Ru( -Cl)Cl]2 (arene = C6H6, p-iPrC6H4Me and C6Me6) with the same ligands (L1 or L2) gives
only the dinuclear complexes [{(
6-C6H6)RuCl}2( -L)]2+ {L = L1 (9); L2 (10)}, [{( 6-p-iPrC6H4Me)R-
uCl}2(
-L)]2+ {L = L1 (11); L2 (12)} and [{( 6-C6Me6)RuCl}2( -L)]2+ {L = L1 (13); L2 (14)}. All complexes
g
5-C5Me5)M(
l
-Cl)Cl]2 (M = Rh and Ir) in the presence of NH4PF6 results
5-C5Me5)RhCl(L)]+ {L = L1 (1);
-L)]2+ {L = L1 (5); L2 (6)},
g
Available online 13 February 2010
g
g
l
g
l
Keywords:
g
l
Arene-ligands
Bis(pyrazolyl)methane
Ruthenium
g
l
g
l
g
l
were isolated as their hexafluorophosphate salts. The single-crystal X-ray crystal structure analyses of
[7](PF6)2, [9](PF6)2 and [11](PF6)2 reveal a typical piano-stool geometry around the metal centers with
six-membered metallo-cycle in which the 1,4-bis{bis(pyrazolyl)-methyl}benzene acts as a bis-bidentate
chelating ligand.
Rhodium
Iridium
Ó 2010 Elsevier B.V. All rights reserved.
1. Introduction
(third-generation) has yet to be explored. Arene ruthenium, rho-
dium and iridium complexes of bis(pyrazolyl)methanes have at-
The coordination chemistry of poly(pyrazolyl)borate and meth-
ane ligands has revealed an impressive number of compounds with
interesting structural, catalytic, and electronic properties [1–6].
The chemistry of poly(pyrazolyl)methane ligands is less extensive
than that of their borate analogues due to the fact that convenient
synthetic routes of functionalized neutral methane species have
only recently been developed [7–10]. By functionalizing the pyra-
zolyl groups in the original poly(pyrazolyl)borate and -methane
compounds, a multitude of ‘‘second-generation” ligands have been
prepared [1–6]. More recently, functionalization of the borate or
methane backbone has yielded a variety of ‘‘third-generation” li-
gands [11] as bis- and tris(pyrazolyl)methane compounds where
two or more of the methane units are linked through organic spac-
ers of varying degrees of flexibility, resulting in multitopic ligands.
The chemistry of ‘‘second generation” bis(pyrazolyl)methane
complexes of rhodium, iridium and ruthenium is relatively less
studied as compared to borate complexes of rhodium and iridium
[11–13]. Indeed, the chemistry of arene ruthenium and penta-
methylcyclopentadienyl (Cp*) rhodium and iridium complexes of
tracted attention due to their catalytic ability in reactions such as
the alcoholysis of ketones and silanes, hydroformylation and
hydroaminomethylation of alkenes and hydroamination [14–16].
Besides these, nitrogen donor ligands with platinum group metals
have been shown to be effective catalysts for oxidation reactions
[17] and for ring-opening metathesis polymerization [18] and
recent studies of arene ruthenium complexes have shown that
they are found to inhibit cancer cell growth [19,20].
In recent years, we have been carrying out arene ruthenium and
Cp* rhodium and iridium complexation reactions with a variety of
nitrogen-based ligands [21–27] including pyrazolyl-pyrimidine,
pyrazolyl-pyridazine and pyridyl-pyridazine ligands. All of these li-
gands after coordination with metal have given five membered che-
lating complexes; this is the first time that isolated six-membered
chelating complexes with 1,4-bis{bis(pyrazolyl)-methyl}benzene
(L1) or 1,4-bis{bis(3-methylpyrazolyl)methyl}benzene (L2) (Chart
1) ligands have been isolated with these metal complexes.
In the present paper, we have synthesized homogeneous and
immobilized half-sandwich rhodium, iridium and ruthenium com-
plexes bearing bis(pyrazolyl)methanes bridged by benzene-linker,
as bidentate or tetradentate bridging ligands (L). The Cp* rhodium
and iridium complexes with ligands L give both mono and dinucle-
ar complexes, while only dinuclear complexes are obtained with
bis(pyrazolyl)methane ligands bridged by
a benzene-linker
* Corresponding author. Tel.: +91 364 272 2620; fax: +91 364 272 1010.
E-mail address: mohanrao59@gmail.com (K.M. Rao).
0022-328X/$ - see front matter Ó 2010 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2010.02.005

1376
K.T. Prasad et al. / Journal of Organometallic Chemistry 695 (2010) 1375–1382
Chart 1.
arene ruthenium complexes. All these complexes are characterized
by IR, NMR, mass spectrometry and UV–Vis spectroscopy. The
molecular structures of three representative complexes are pre-
sented as well.
(d, 2H, J = 6.8 Hz, C6H4), 6.41–6.37 (m, 4H, pz-4H), 2.61 (bs, 6H,
Pz-3Me), 2.38 (bs, 6H, Pz-3Me), 1.58 (s, 15H, C5Me5); IR (KBr,
cmꢀ1): 3441(w), 3134(m), 1629(m), 1447(m), 1399(m), 1296(m),
1103(m), 845(s), 760(m), 558(m); ESI-MS: 700.6 [M+], 675.6
[MꢀCl]; UV–Vis {acetonitrile, kmax nm (
e
10ꢀ5 Mꢀ1 cmꢀ1)}: 229
(0.43), 394 (0.22); Anal. Calc. for C34H41F6RhN8PCl (845.6): C,
2. Experimental
48.32; H, 4.89; N, 13.26. Found: C, 48.23; H, 4.91; N, 13.18%.
2.1. General remarks
2.2.3. [(g
5-C5Me5)Ir(L1)Cl]PF6 ([3]PF6)
Yield: 90 mg (64%). 1H NMR (400 MHz, CD3CN) d = 8.26 (s, 1H,
CH(pz)2), 7.99 (d, 2H, J = 1.80 Hz, pz-5H), 7.87 (d, 2H, J = 2.40 Hz,
pz-3H), 7.78 (s, 1H, CH(pz)2), 7.61 (d, 2H, J = 1.2 Hz, pz-5H), 7.50
(d, 2H, J = 2.40 Hz, pz-3H), 7.05 (d, 2H, J = 7.2 Hz, C6H4), 6.75 (d,
2H, J = 6.8 Hz, C6H4), 6.39–6.36 (m, 4H, pz-4H), 1.52 (s, 15H,
C5Me5); IR (KBr, cmꢀ1): 3448(w), 3134(m), 1627(m), 1446(m),
1399(m), 1296(m), 1103(m), 843(s), 760(m), 558(m); ESI-MS:
All reagents were purchased either from Aldrich or Fluka and
used as received. All the experiments were performed under nor-
mal conditions. The ligands 1,4-bis{bis(pyrazolyl)-methyl}benzene
(L1) and 1,4-bis{bis(3-methylpyrazolyl)methyl}benzene (L2), were
synthesized by reported procedure [28] The dinuclear complexes
[(
g
6-C6H6)Ru(
l
-Cl)Cl]2, [(
g
6-p-iPrC6H4Me)Ru(
l
-Cl)Cl]2 and [(g6
-Cl)Cl]2 (M = Rh
-
C6H6)Ru(
l
-Cl)Cl]2 [29–31], and [(
g
5-C5Me5)M(
l
733.3 [M+], 698.1 [MꢀCl]; UV–Vis {acetonitrile, kmax nm
(e
and Ir) [32–34], were prepared according to literature methods.
NMR spectra were recorded on Bruker AMX-400 MHz spectrome-
ter. Infrared spectra were recorded as KBr pellets on a Perkin–El-
mer 983 spectrophotometer. Elemental analyses were performed
on a Perkin–Elmer-2400 CHN/S analyzer. Mass spectra were ob-
tained from Waters ZQ-4000 mass spectrometer by ESI method.
Absorption spectra were obtained at room temperature using a
Perkin–Elmer Lambda 25 UV–Vis spectrophotometer.
10ꢀ5 Mꢀ1 cmꢀ1)}: 225(0.73), 352 (0.038); Anal. Calc. for
C30H33F6N8PIrCl (878.5): C, 41.03; H, 3.79; N, 12.76. Found: C,
43.93; H, 3.73; N, 12.65%.
2.2.4. [(g
5-C5Me5)Ir(L2)Cl]PF6 ([4]PF6)
Yield 89 mg (60%). 1H NMR (400 MHz, CD3CN) d = 8.27 (s, 1H,
CH(pz)2), 8.02 (d, 2H, J = 1.80 Hz, pz-5H), 7.76 (s, 1H, CH(pz)2),
7.62 (d, 2H, J = 1.2 Hz, pz-5H), 7.09 (d, 2H, J = 7.2 Hz. C6H4), 6.78
(d, 2H, J = 6.8 Hz, C6H4), 6.42–6.36 (m, 4H, pz-4H), 2.63 (s, 6H,
Pz-3Me), 2.37 (s, 6H, Me3-Pz), 1.55 (s, 15H, C5Me5); IR (KBr,
cmꢀ1): 3441(w), 3134(m), 1629(m), 1447(m), 1399(m), 1296(m),
1103(m), 845(s), 760(m), 558(m); ESI-MS: 789.4 [M+], 754.2
2.2. General procedure for the syntheses of the mononuclear complexes
1–4
A mixture of [(g l-Cl)Cl]2 (M = Rh, Ir) (0.08 mmol),
5-C5Me5)M(
[MꢀCl]; UV–Vis {acetonitrile, kmax nm (
e
10ꢀ5 Mꢀ1 cmꢀ1)}: 228
(0.51), 485 (0.02); Anal. Calc. for C34H41F6IrN8PCl (934.8): C,
ligand L (L1 or L2) (0.17 mmol) and 2.5 equiv of NH4PF6 in dry
methanol (20 ml) was refluxed at 50 °C for 6–8 h, after which an
orange precipitate was observed. The precipitate was separated
by filtration, washed with cold methanol, diethyl ether and dried
in vacuo.
43.70; H, 4.42; N, 11.99. Found: C, 43.67; H, 4.49; N, 11.86%.
2.3. General procedure for the syntheses of the dinuclear complexes
5–8
2.2.1. [(g
5-C5Me5)Rh(L1)Cl]PF6 ([1]PF6)
Yield: 90 mg (72%). 1H NMR (400 MHz, CD3CN) d = 8.29 (s, 1H,
CH(pz)2), 8.05 (d, 2H, J = 1.80 Hz, pz-5H), 7.91 (d, 2H, J = 2.40 Hz,
pz-3H), 7.78 (s, 1H, CH(pz)2), 7.64 (d, 2H, J = 1.2 Hz, pz-5H), 7.58
(d, 2H, J = 2.40 Hz, pz-3H), 7.05 (d, 2H, J = 7.2 Hz, C6H4), 6.75 (d,
2H, J = 6.8 Hz, C6H4), 6.41–6.38 (m, 4H, pz-4H), 1.54 (s, 15H,
C5Me5); IR (KBr, cmꢀ1): 3441(w), 3134(m), 1629(m), 1447(m),
1399(m), 1296(m), 1103(m), 845(s), 760(m), 558(m); ESI-MS:
643.8 [M+], 608.5 [MꢀCl]; UV–Vis {acetonitrile, kmax nm
A mixture of [(Cp*)M(l-Cl)Cl]2 (M = Rh, Ir) (0.08 mmol), ligand L
(L1 or L2) (0.08 mmol) and 2.5 equiv of NH4PF6 in dry methanol
(20 ml) was refluxed at 50 °C for 12 h, after which a dark orange
precipitate was formed. The precipitate was separated by filtration,
washed with cold methanol, diethyl ether and dried in vacuo.
2.3.1. [{(g l-L1)](PF6)2 ([5](PF6)2)
5-C5Me5)RhCl}2(
Yield 80 mg (84%). 1H NMR (400 MHz, CD3CN) d = 8.31 (s, 2H,
CH(pz)2), 8.09 (d, 4H, J = 1.60 Hz, pz-5H), 7.95 (d, 4H, J = 2.11 Hz,
pz-3H), 6.76 (s, 4H, C6H4), 6.41 (dd, 4H, J = 1.20 Hz, pz-4H), 1.48
(s, 30H, C5Me5); IR (KBr, cmꢀ1): 3446(w), 3134(m), 1629(m),
1446(m), 1401(m), 1295(m), 1103(m), 843(s), 760(m), 555(m);
ESI-MS: 1062.6 [M2++PF6ꢀ]+; UV–Vis {acetonitrile, kmax nm
(
e
10ꢀ5 Mꢀ1 cmꢀ1)}: 223 (0.59), 341 (0.04); Anal. Calc. for
C30H33F6N8PRhCl (788.9): C, 45.67; H, 4.22; N 14.20. Found: C,
45.53; H, 4.23; N, 14.13%.
2.2.2. [(g
5-C5Me5)Rh(L2)Cl]PF6 ([2]PF6)
Yield 99 mg (74%). 1H NMR (400 MHz, CD3CN) d = 8.31 (s, 1H,
CH(pz)2), 8.01 (d, 2H, J = 1.80 Hz, pz-5H), 7.81 (s, 1H, CH(pz)2),
7.62 (d, 2H, J = 1.2 Hz, pz-5H), 7.07 (d, 2H, J = 7.2 Hz, C6H4), 6.76
(e
10ꢀ5 Mꢀ1 cmꢀ1)}: 224 (0.54), 307 (0.05) and 437 (0.01); Anal.
Calc. for C40H48F12N8P2Rh2Cl2 (1207.6): C, 39.79; H, 4.01; N, 9.28.
Found: C, 39.53; H, 4.06; N, 9.19%.

K.T. Prasad et al. / Journal of Organometallic Chemistry 695 (2010) 1375–1382
1377
2.3.2. [{(g5-Cp )RhCl}2(
l
-L2)](PF6)2 ([6](PF6)2)
2.4.3. [{(g l-L1)](PF6)2 ([11](PF6)2)
6-p-iPrC6H4Me)RuCl}2(
*
Yield 80 mg (84%). 1H NMR (400 MHz, CD3CN) 8.33 (s, 2H,
CH(pz)2), 8.07 (d, 4H, J = 1.64 Hz, pz-5H), 6.78 (s, 4H, C6H4), 6.39
(dd, 4H, J = 1.20 Hz, pz-4H), 2.76 (s, 12H, pz-3Me), 1.49 (s, 30H,
C5Me5); IR (KBr, cmꢀ1): 3446(b), 3131(m), 1627(m), 1446(m),
1408(m), 1296(m), 1103(m), 845(s), 761(m), 585(m); ESI-MS:
Yield 91 mg (81%). 1H NMR (400 MHz, CD3CN) d = 8.32 (s, 2H,
CH(pz)2), 8.04 (d, 4H, J = 1.40 Hz, pz-5H), 7.95 (d, 4H, J = 2.04 Hz,
pz-3H), 6.76 (s, 4H, C6H4), 6.41 (dd, 4H, J = 1.28 Hz, pz-4H), 5.57
(d, 4H, J = 5.60 Hz, Arp-cy), 5.38 (d, 4H, J = 5.80 Hz, Arp-cy), 2.84 (sept,
2H, CH(CH3)2), 2.17 (s, 6H, Arp-cy-Me), 1.25 (d, 6H, CH(CH3)2); 1.21
(d, 6H, CH(CH3)2); IR (KBr, cmꢀ1): 3441(b), 3134(m), 1629(m),
1447(m), 1399(m), 1296(m), 1103(m), 845(s), 760(m), 558(m);
1118.6 [M2++PF6ꢀ]+; UV–Vis {acetonitrile, kmax nm
(e
10ꢀ5 Mꢀ1 cmꢀ1)}: 228 (0.59), 310 (0.04) and 430 (0.02); Anal. Calc.
for C44H56Cl2F12N4P2Rh2 (1263.6): C, 41.82; H, 4.47; N, 8.87. Found:
C, 41.71; H, 4.55; N, 8.65%.
ESI-MS: 1056.2 [M2++PF6ꢀ]+; UV–Vis {acetonitrile, kmax nm (
e
10ꢀ5 Mꢀ1 cmꢀ1)}: 224 (0.65), 316 (0.05) and 431 (0.02); Anal. Calc.
for C40H46Cl2F12N8P2Ru2 (1201.8): C, 39.97; H, 3.86; N, 9.32. Found:
C, 39.78; H, 3.97; N, 9.27%.
2.3.3. [{(g l-L1)](PF6)2 ([7](PF6)2)
5-C5Me5)IrCl}2(
Yield 91 mg (77%). 1H NMR (400 MHz, CD3CN) d = 8.32 (s, 2H,
CH(pz)2), 8.06 (d, 4H, J = 1.62 Hz, pz-5H), 8.01 (d, 4H, J = 2.16 Hz,
pz-3H), 6.78 (s, 4H, C6H4), 6.44 (dd, 4H, J = 1.22 Hz, pz-4H), 1.51
(s, 30H, C5Me5); IR (KBr, cmꢀ1): 3441(b), 3134(m), 1629(m),
1447(m), 1399(m), 1296(m), 1103(m), 845(s), 760(m), 558(m);
ESI-MS: 1241.5 [M2++PF6ꢀ]+; UV–Vis {acetonitrile, kmax nm
2.4.4. [{(g l-L2)](PF6)2 ([12](PF6)2)
6-p-iPrC6H4Me)RuCl}2(
Yield 79 mg (63%). 1H NMR (400 MHz, CD3CN) d = 8.34 (s, 2H,
CH(pz)2), 8.03 (d, 4H, J = 1.40 Hz, pz-5H), 6.76 (s, 4H, C6H4), 6.41
(d, 4H, J = 3.20 Hz, pz-4H), 5.55 (d, 4H, J = 5.60 Hz, Arp-cy), 5.39 (d,
4H, J = 5.80 Hz, Arp-cy), 2.87 (s, 12H, pz-3Me), 2.79 (sept, 2H,
CH(CH3)2), 2.16 (s, 6H, Arp-cy-Me), 1.26 (d, 6H, CH(CH3)2); 1.21 (d,
6H, CH(CH3)2); IR (KBr, cmꢀ1): 3446(b), 3134(m), 1627(m),
1448(m), 1399(m), 1296(m), 1105(m), 843(s), 762(m), 558(m);
ESI-MS: 1112.2 [M2++PF6ꢀ]+; UV–Vis {acetonitrile, kmax nm
(e
10ꢀ5 Mꢀ1 cmꢀ1)}: 225 (0.58), 312 (0.04) and 391 (0.03); Anal.
Calc. for C40H48Cl2F12Ir2N8P2 (1386.2): C, 34.66; H, 3.49; N, 8.08.
Found: C, 34.42; H, 3.52; N, 8.01%.
(e
10ꢀ5 Mꢀ1 cmꢀ1)}: 229 (0.56), 307 (0.05) and 437 (0.02); Anal.
Calc. for C44H54Cl2F12N4P2Ru2 (1257.9): C, 42.01; H, 4.33; N, 8.91.
Found: C, 41.93; H, 4.36; N, 8.87%.
2.3.4. [{(g l-L2)](PF6)2 ([8](PF6)2)
5-C5Me5)IrCl}2(
Yield 81 mg (65%). 1H NMR (400 MHz, CD3CN) d = 8.33 (s, 2H,
CH(pz)2), 8.09 (d, 4H, J = 1.60 Hz, pz-5H), 6.74 (s, 4H, C6H4), 6.44
(dd, 4H, J = 1.20 Hz, pz-4H), 2.76–2.80 (s, 12H, pz-3Me), 1.48 (s,
30H, C5Me5); IR (KBr, cmꢀ1): 3446(b), 3134(m), 1629(m),
1446(m), 1401(m), 1295(m), 1103(m), 843(s), 760(m), 558(m);
ESI-MS: 1297.5 [M2++PF6ꢀ]+; UV–Vis {acetonitrile, kmax nm
2.4.5. [{(g l-L1)](PF6)2 ([13](PF6)2)
6-C6Me6)RuCl}2(
Yield 101 mg (80%). 1H NMR (400 MHz, CD3CN) d = 8.35 (s, 2H,
CH(pz)2), 8.07 (d, 4H, J = 1.40 Hz, pz-5H), 7.97 (d, 4H, J = 2.00 Hz,
pz-3H), 6.75 (s, 4H, C6H4), 6.44 (dd, 4H, J = 1.24 Hz, pz-4H), 2.28
(s, 36H, C6Me6); IR (KBr, cmꢀ1): 3441(b), 3134(m), 1629(m),
1447(m), 1399(m), 1296(m), 1103(m), 845(s), 760(m), 558(m);
ESI-MS: 1112.8 [M2++PF6ꢀ]+; UV–Vis {acetonitrile, kmax nm
(e
10ꢀ5 Mꢀ1 cmꢀ1)}: 228 (0.71), 316 (0.04) and 397 (0.02); Anal.
Calc. for C44H56Cl2F12Ir2N8P2 (1442.2): C, 36.64; H, 3.91; N, 7.77.
Found: C, 36.62; H, 3.99; N, 7.65%.
(e
10ꢀ5 Mꢀ1 cmꢀ1)}: 228 (0.68), 312 (0.05) and 427 (0.02); Anal.
Calc. for C44H54Cl2F12N8P2Ru2 (1257.9): C, 42.01; H, 4.33; N, 8.91.
Found: C, 42.05; H, 4.41; N, 8.88%.
2.4. General procedure for the synthesis of the dinuclear complexes 9–
14
A
mixture
of
[(
g
6-arene)Ru(
l-Cl)Cl]2
(arene = C6H6,
p-iPrC6H4Me or C6Me6) (0.1 mmol), ligand L (L1 or L2) (0.1 mmol)
and 2.5 equiv of NH4PF6 in dry methanol (15 ml) was stirred at
room temperature for 10 h, after which an orange precipitate
was observed. The precipitate was filtered, washed with cold
methanol, diethyl ether and dried in vacuo.
2.4.6. [{(g l-L2)](PF6)2 ([14](PF6)2)
6-C6Me6)RuCl}2(
Yield 86 mg (65%). 1H NMR (400 MHz, CD3CN) d = 8.36 (s, 2H,
CH(pz)2), 8.07 (d, 4H, J = 1.40 Hz, pz-5H), 6.78 (s, 4H, C6H4), 6.46
(d, 4H, J = 2.24 Hz, pz-4H), 2.85 (s, 12H, pz-3Me), 2.26 (s, 36H,
C6Me6); IR (KBr, cmꢀ1): 3446(b), 3135(m), 1626(m), 1446(m),
1402(m), 1296(m)ꢀ, 1103(m), 844(s), 760(m), 558(m); ESI-MS:
[M2++PF6 ]+;
UV–Vis
{acetonitrile,
kmax
nm
2.4.1. [{(g l-L1)](PF6)2 ([9](PF6)2)
6-C6H6)RuCl}2(
1169.8
(e
10ꢀ5 Mꢀ1 cmꢀ1)}: 229 (0.71), 317 (0.04) and 397 (0.03); Anal.
Yield 80 mg (72%). 1H NMR (400 MHz, CD3CN) d = 8.26 (s, 2H,
CH(pz)2), 8.07 (d, 4H, J = 1.40 Hz, pz-5H), 7.95 (d, 4H, J = 2.00 Hz,
pz-3H), 6.75 (s, 4H, C6H4), 6.41 (dd, 4H, J = 1.24 Hz, pz-4H), 5.40
(s, 12H, C6H6); IR (KBr, cmꢀ1): 3441(b), 3134(m), 1629(m),
1447(m), 1399(m), 1296(m), 1103(m), 845(s), 760(m), 558(m);
ESI-MS: 944.8 [M2++PF6ꢀ]+; UV–Vis {acetonitrile, kmax nm
Calc. for C48H62Cl2F12N8P2Ru2 (1314.1): C, 43.87; H, 4.76; N, 8.53.
Found: C, 43.75; H, 4.75; N, 8.52%.
2.5. Single-crystal X-ray structure analyses
(e
10ꢀ5 Mꢀ1 cmꢀ1)}: 226 (0.73), 307 (0.05) and 428 (0.01); Anal.
Calc. for C32H30Cl2F12N8P2Ru2 (1089.6): C, 35.27; H, 2.78; N,
10.28. Found: C, 35.15; H, 2.81; N, 10.18%.
Crystals of complexes [7](PF6)2, [9](PF6)2 and [11](PF6)2 were
mounted on a Stoe Image Plate Diffraction system equipped with
a u circle goniometer, using Mo-Ka graphite monochromated radi-
ation (k = 0.71073 Å) with u range 0–200°. The structures were
solved by direct methods using the program SHELXS–97 [35]. Refine-
ment and all further calculations were carried out using SHELXL-97
[36]. The H-atoms were included in calculated positions and trea-
ted as riding atoms using the SHELXL default parameters. The non-H
atoms were refined anisotropically, using weighted full-matrix
least-square on F2. In [7](PF6)2ꢁ2CH3CN, the residual electron den-
sities greater than 1 e Åꢀ3 are all located at less than 1 Å from the
iridium atoms. Crystallographic details are summarized in Table 1
and selected bond lengths and angles are presented in Table 2. Figs.
1–3 were drawn with ORTEP–32 [37].
2.4.2. [{(g l-L2)](PF6)2 ([10](PF6)2)
6-C6H6)RuCl}2(
Yield 76 mg (66%). 1H NMR (400 MHz, CD3CN) d = 8.31 (s, 2H,
CH(pz)2), 8.07 (d, 4H, J = 1.40 Hz, pz-5H), 6.78 (s, 4H, C6H4), 6.46
(dd, 4H, J = 1.24 Hz, pz-4H), 5.48 (s, 12H, C6H6), 2.86 (s, 12H, pz-
3Me); IR (KBr, cmꢀ1): 3448(b), 3134(m), 1627(m), 1446(m),
1399(m), 1296(m), 1103(m), 843(s), 760(m), 558(m); ESI-MS:
1000.2 [M2++PF6ꢀ]+; UV–Vis {acetonitrile, kmax nm ( 10ꢀ5 Mꢀ1 cmꢀ1)}:
e
229 (0.65), 316 (0.05) and 430 (0.02); Anal. Calc. for
C36H38Cl2F12N8P2Ru2 (1145.7): C, 37.74; H, 3.34; N, 9.78. Found: C,
37.65; H, 3.35; N, 9.65%.

1378
K.T. Prasad et al. / Journal of Organometallic Chemistry 695 (2010) 1375–1382
Table 1
Crystallographic and structure refinement parameters for complexes [7](PF6)2ꢁ2CH3CN, [9](PF6)2ꢁCH3CN and [11](PF6)2ꢁ2CH3CN.
[7](PF6)2ꢁ2CH3CN
[9](PF6)2ꢁCH3CN
[11](PF6)2ꢁ2CH3CN
Chemical formula
Formula weight
C44H54Cl2F12Ir2N10P2
1468.21
C34H33Cl2F12N10P2Ru2
1130.67
C44H52Cl2F12N10P2Ru2
1283.94
Crystal system
Space group
Crystal color and shape
Crystal size
a (Å)
b (Å)
c (Å)
Monoclinic
P21/n (no. 14)
Orange block
0.27 ꢂ 0.24 ꢂ 0.22
13.6968(13)
14.0285(9)
14.5963(14)
114.169(10)
2558.8(4)
Monoclinic
P21/n (no. 14)
Orange block
0.25 ꢂ 0.22 ꢂ 0.18
15.3761(9)
13.9492(10)
19.9223(13)
105.567(7)
4116.3(5)
Monoclinic
P21/c (no. 14)
Orange block
0.23 ꢂ 0.19 ꢂ 0.15
9.4659(7)
25.737(2)
11.0998(9)
110.868(9)
2526.8(3)
b (°)
V (Å3)
Z
2
4
2
T (K)
173(2)
1.906
5.45
173(2)
1.824
1.036
173(2)
1.688
0.855
Dcalc (g cmꢀ3
)
l
(mmꢀ1
)
Scan range (°)
Unique reflections
Reflections used [I > 2
Rint
2.11 < h < 26.18
5045
3675
2.09 < h < 26.04
8055
4212
2.12 < h < 26.04
4849
3295
r
(I)]
0.0745
0.0944
0.0591
Final R indices [I > 2
R indices (all data)
Goodness-of-fit
r
(I)]a
0.0415, wR2 0.1038
0.0616, wR2 0.1103
0.927
0.0428, wR2 0.0789
0.0982, wR2 0. 0872
0.797
0.952, ꢀ0.929
0.0463, wR2 0.1189
0.0704, wR2 0.1269
0.961
1.538, ꢀ0.792
Max, Min
D
q
/e (Åꢀ3
)
3.086, ꢀ2.055
P
P
P
2
2
1=2
2
Structures were refined on F02 : wR2 ¼ ½ ½wðF02 ꢀ Fc2Þ ꢃ= wðF02Þ ꢃ , where wꢀ1 ¼ ½ ðF20Þ þ ðaPÞ þ bPꢃ and P ¼ ½maxðF02; 0Þ þ 2F2c ꢃ=3.
a
5-C5Me5)M(
l
-Cl)Cl]2 (M = Rh, Ir) with two equiva-
Table 2
complexes [(
g
Selected bond lengths and angles for complexes [7](PF6)2ꢁ2CH3CN, [9](PF6)2ꢁCH3CN
lents of ligands L1 or L2 in methanol. These complexes are iso-
lated as their hexafluorophosphate salts and complexes 1–4 are
orange/red, non-hygroscopic, and air-stable, shiny crystalline sol-
ids. They are sparingly soluble in methanol, dichloromethane,
chloroform and acetone, but well soluble in acetonitrile and
dimethylsulphoxide.
and [11](PF6)2ꢁ2CH3CN.
[7](PF6)2
Inter atomic distances (Å)
M–M
M–N1
M–N3
M–N5
M–N7
M–Cl1
M–Cl2
M-centroida
N1–N2
N3–N4
N5–N6
N7–N8
[9](PF6)2
[11](PF6)2
9.4781(9)
2.110(6)
2.093(6)
8.8236(8)
2.086(4)
2.089(5)
2.081(4)
2.085(5)
2.395(2)
2.392(2)
1.668
1.352(6)
1.358(7)
1.366(6)
1.366(6)
8.8285(13)
2.102(4)
2.098(4)
3.2. Characterization of the mononuclear complexes 1–4
2.394(2)
2.391(1)
All these mononuclear complexes were characterized by IR, 1H
NMR, mass and elemental analysis. The infrared spectra of the
complexes 1–4 exhibit a strong band in the region 844–850 cmꢀ1
1.788
1.345(8)
1.372(8)
1.673
1.351(6)
1.350(6)
for a typical mP–F stretching band and a medium band in the region
555–558 cmꢀ1 dP-F for the PF6 anion. Moreover, all complexes show
absorption bands around 1620–1631, 1446–1458, 1270–1296 and
1103–1058 cmꢀ1 corresponding to mC@N vibrations of pyrazoles
[38,39]. Besides these absorptions, two absorption bands at
2990–3050 cmꢀ1 and 3400–3450 cmꢀ1 were also observed for N–
H vibrations. The mass spectra of these complexes 1–4 exhibit
the corresponding molecular ion peaks at m/z = 643, 700, 733
and 789.
Angles (°)
N1–M–N3
N5–M–N7
N1–M–Cl1
N3–M–Cl1
N5–M–Cl2
N7–M–Cl2
M–N1–N2
M–N3–N4
M–N5–N6
M–N7–N8
86.0(2)
84.31(17)
85.08(16)
83.82(17)
84.01(17)
83.36(18)
84.42(13)
84.80(13)
84.54(12)
84.77(13)
124.6(3)
125.4(3)
125.4(3)
125.5(3)
85.20(11)
83.15(11)
125.4(5)
125.9(5)
126.2(3)
125.2(3)
The 1H NMR spectra of free ligand (L1 or L2) exhibit a character-
istic set of five resonances for the pyrazole, methyl and benzene
ring protons. However the 1H NMR spectrum of L2 ligand shown
two types of isomers, they are 3 and 5-methyl substituted pyra-
zoles. From the proton NMR studies indicated the ratio of 3 and
5 isomers are 78% and 22%, respectively, since it was prepared from
terphthaldehyde and 3-methyl-pyrazole [28]. Upon formation of
the complexes with this ligand (L2), the detection of signals of 5
methyl isomer is not noticed in the NMR spectrum due to the dom-
ination of 3 methyl substituted pyrazole NMR signals. So the signal
intensity of later isomer (5-methyl substituted pyrazole) is so
small and difficult to assign methyl protons in all the complexes.
The mononuclear cationic complexes 1–4 exhibit ten distinct reso-
nances assignable to pyrazole or methyl-pyrazole and benzene ring
protons of the (L1 or L2) ligand indicating formation of mononu-
clear complexes. The methylic proton {–CH(Pz)2–} of ligand has
shown two singlets at d = 8.29 and 7.78 corresponding to coordi-
nated and uncoordinated to the metal complex indicating
a
Calculated centroid-to-metal distances (g g
6-C6 or 5-C5 coordinated aromatic
ring).
3. Results and discussion
3.1. Synthesis of the mononuclear complexes 1–4 as
hexafluorophosphate salts
The mononuclear cationic pentamethylcyclopentadienyl
rhodium and iridium complexes having 1,4-bis{bis(pyrazolyl)-
methyl}benzene (L1) and 1,4-bis{bis(3-methylpyrazolyl)methyl}-
benzene (L2) ligands viz., [(
(2)}, [(
5-C5Me5)IrCl(L)]+ {L = L1 (3), L2 (4)} (Scheme 1), have
been prepared by the reaction of pentamethylcyclopentadienyl
g
5-C5Me5)RhCl(L)]+ {L = L1 (1), L2
g

K.T. Prasad et al. / Journal of Organometallic Chemistry 695 (2010) 1375–1382
1379
Scheme 1.
formation of mono nuclear compounds. Besides these resonances
3.4. Characterization of the dinuclear complexes 5–14
complexes 1–4 exhibit a singlet at d ꢄ 1.5 for the protons of the
pentamethylcyclopentadienyl ligand.
Infrared spectra of the dinuclear complexes 5–14 show a similar
trend as the mononuclear cationic complexes 1–4. The mass spec-
tra of the complexes 5–14 give rise to two main peaks; a minor
peak with an approximately 50% intensity attributed to
[M2++PFꢀ6 ]+ at m/z 1062, 1118, 1241, 1297, 944, 1000, 1056, 1112,
1112 and 1169, respectively, and a major peak, which corresponds
to loss of [(Cp*/arene)MCl]+ fragment and the formation of mono-
nuclear cations 1–6 at m/z = 643, 700, 733, 789, 585, 641, 641, 697,
669 and 725, respectively.
3.3. Synthesis of dinuclear complexes 5–14 as hexafluorophosphate
salts
The reaction of the chloro bridged dinuclear complexes
[(g l-Cl)Cl]2 (M = Rh, Ir); [(g l-Cl)Cl]2 (are-
5-C5Me5)M( 6-arene)Ru(
ne = C6H6, p-iPrC6H4Me and C6Me6) with 1 equiv of 1,4-bis{bis(pyr-
azolyl)-methyl}benzene (L1) or 1,4-bis{bis(3-methylpyrazolyl)
methyl}-benzene (L2) in methanol results in the formation of or-
The 1H NMR spectra of the dinuclear dicationic complexes 5–14
exhibited five distinct resonances assignable to pyrazole rings,
methyl and benzene ring protons of the ligands (L1 or L2) indicat-
ing formation of dinuclear complexes. The methylic proton
{–CH(Pz)2–} of ligand has exhibited a singlet at d = 8.36–8.33 indi-
cating formation of dinuclear compounds. Besides these reso-
nances complexes 5–8 exhibit a singlet at d ꢄ 1.5 for the protons
of the pentamethylcyclopentadienyl ligands. Interestingly, in these
complexes the chemical shift of the protons of the pentamethylcy-
clopentadienyl ligands does not show downfield shift as like with
ange, air-stable, dinuclear dicationic complexes [{(
RhCl}2(
-L)]2+ {L = L1 (5); Lp2 (6)}, [{( 5-C5Me5)IrCl}2(
{L = L1 (7); L2 (8)}, [{(
6-C6H6)RuCl}2( -L)]2+ {L = L1 (9); L2 (10)},
[{(
6-p-iPrC6H4Me)RuCl}2( -L)]2+ {L = L1 (11); L2 (12)} and [{(g6
C6H6)RuCl}2(
-L)]2+ {L = L1 (13); L2 (14)}. All complexes are iso-
g
5-C5Me5)
-L)]2+
l
g
l
g
l
g
l
-
l
lated as their hexafluorophosphate salts (Scheme 2) and they are
characterized by IR, mass, 1H NMR spectrometry, UV–Vis spectros-
copy, and elemental analysis.
Scheme 2.

1380
K.T. Prasad et al. / Journal of Organometallic Chemistry 695 (2010) 1375–1382
other nitrogen-based ligands [21–27]. Complexes 9 and 10 exhibit
a singlet at d = 5.40 and 5.48 for protons of benzene ligands, com-
plexes 11 and 12 exhibits a doublet at d = 1.21 for the protons of
the isopropyl methyl groups, a singlet at d = 1.26 for the methyl
protons, a septet at d = 2.79 for the proton of the isopropyl group.
The two doublets centered at d ꢄ 5.55 and 5.38 correspond to the
CH aromatic protons of the p-cymene rings. Complexes 13–14 ex-
hibit a strong peak at d = 2.25 for the methyl protons of hexameth-
3.5. Crystal structure analysis of [{(
([7](PF6)2), [{(
6-C6H6)RuCl}2( -L1)]2+ ([9](PF6)2) and
[{(
6-p-iPrC6H4Me)RuCl}2( -L1)]2+ ([11](PF6)2)
g l
5-C5Me5)IrCl}2( -L1)]2+
g
l
g
l
The molecular structure of complexes [{(
-L1)]2+ ([7](PF6)2), [{( 6-C6H6)RuCl}2( -L1)]2+ ([9](PF6)2) and
[{(
6-p-iPrC6H4Me)RuCl}2( -L1)]2+ ([11](PF6)2) were determined
g
5-C5Me5)IrCl}2
(l
g
l
g
l
by single crystal X-ray diffraction analysis. The crystallographic
data are gathered in Table 1 and the selected bond lengths and
angles for complexes [7](PF6)2, [9](PF6)2 and [11](PF6)2 are pre-
sented in Table 2. The corresponding ORTEP drawings are shown
in Figs. 1, 2 and 3, respectively. All complexes show typical pia-
no-stool geometry and have a half-sandwich structure consisting
*
ylbenzene ligand. In similar case with the Cp analogues the arene
ruthenium complexes also the chemical shifts of the arene ligands
of ruthenium does not shifted down filed as compared to other N-
based ligands, this could be due to the geometrical orientation of
arene ligands to the benzene-linker [24–27].
Fig. 1. ORTEP diagram with labelling scheme for [7](PF6)2ꢁ2CH3CN, at 50% probability level, PF6 anions and acetonitrile molecules omitted for clarity (symmetry code:
i = 2 ꢀ x, 2 ꢀ y, ꢀz).
Fig. 2. ORTEP diagram with labelling scheme for [9](PF6)2ꢁCH3CN, at 50% probability level, PF6 anions and acetonitrile molecules omitted for clarity.

K.T. Prasad et al. / Journal of Organometallic Chemistry 695 (2010) 1375–1382
1381
of coordinated pentamethylcyclopentadienyl or arene; a chloride
and the ligand through nitrogen’s (see Figs. 1–3).
complex 9 which are ranging from 2.081(4) to 2.089(5) Å, but are
comparable to those found in 11 [2.102(4) and 2.098(4) Å]. All me-
tal-chlorido bond distances are comparable, ranging from 2.391(1)
to 2.395(2) Å, and are almost identical to other reported values
The distance of the iridium atoms and the corresponding cen-
troids of
tween the ruthenium atoms and the centroid of the C6H6 and
6-p-iPrC6H4Me rings in complexes 9 and 11 are almost equivalent
at 1.67 Å. These distances are comparable to those in the related
complex cations [(
6-p-iPrC6H4Me)Ru(2-acetylthiazoleazine)Cl]+
and [{(
6-p-PriC6H4Me)RuCl}2(4,6-bis(3,5-dimethylpyrazolyl)-
g
5-C5Me5 rings is 1.79 Å in complex 7. The distance be-
[24,26]. In all complexes the
g g -
5-C5Me5, 6-C6H6 or g6
g
p-iPrC6H4Me rings are positioned opposite to each other to the
benzene-linker and chlorine atoms of the two metal atoms are lo-
cated at the periphery of the complexes. The N1–Ir1–N3 bond an-
gle in complex 7 is found to be 86.0(2)° and in complexes 9 and 11
are found to be 84.3(2)°, 83.8(2)° and 85.1(2)°, respectively. These
bond angles are comparable to those in the related complex cat-
g
g
pyrimidine)]2+ [24,40]. The average Ir–C distances of complex 7 is
slightly shorter (2.16 Å) than the corresponding Ru–C distances. In-
deed the average Ru–C distances of complex 9 are slightly shorter
(2.17 Å) than the complex 11, which is containing p-cymene ligand
(2.19 Å). Which are almost identical to those reported iridium or
ions [(
(bpzmArNO2]BPh4 [13].
g g
6-C6H6)Ru(bpzmArOCH3)]BPh4 and [( 6-p-iPrC6H4Me)Ru-
All compounds crystallise with acetonitrile molecules, which
surprisingly interact strongly with neither the cation nor the
anions. However, all hydrogen atoms of the tertiary carbons (C7
as well as C14 in 9) are involved in C–Hꢁ ꢁ ꢁF or C–Hꢁ ꢁ ꢁCl interac-
tions in the crystal packing. In [7](PF6)2ꢁ2CH3CN and
[11](PF6)2ꢁ2CH3CN, the Cꢁ ꢁ ꢁF separations are ranging from 3.31 to
rhodium complexes such as [(
ylethylsalicylaldiimine)] [2.17 Å] [41] and [(
Me)Ru(2-(2-thiazolyl)-1,8-naphthyridine)Cl]PF6 [2.19 Å] [26].
The Ir–N bond distances of complex at 2.110(6) and
2.093(6) Å are slightly longer than the Ru–N bond distances of
g
5-C5Me5)IrCl((S)-1-phen-
6-p-iPrC6H4-
g
7
Fig. 3. ORTEP diagram with labelling scheme for [11](PF6)2ꢁ2CH3CN, at 50% probability level, PF6 anions and acetonitrile molecules omitted for clarity (symmetry code: i = ꢀx,
1 ꢀ y, ꢀz).
Fig. 4. UV–Vis electronic spectra of selected complexes (acetonitrile, 10ꢀ5 M, 298 K).

1382
K.T. Prasad et al. / Journal of Organometallic Chemistry 695 (2010) 1375–1382
3.58 Å with C–Hꢁ ꢁ ꢁF angles ranging from 131.3 to 163.1°, while in
[9](PF6)2ꢁCH3CN, the Cꢁ ꢁ ꢁCl distances are 3.40 and 3.43 Å with C–
Hꢁ ꢁ ꢁCl angles of 153.2° and 142.8°, respectively.
data associated with this article can be found, in the online version,
at doi:10.1016/j.jorganchem.2010.02.005.
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3.6. UV–Vis spectroscopy
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Scorpionates:
The
Coordination
Chemistry
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*
ized or intra-ligand
p
?
p
transition in the ultraviolet region
(M) ?
* (L1 –
and metal-to-ligand charge transfer (MLCT) d
p
p
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* orbitals of the ligands. All mononuclear
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gand–localized or intra-ligand
p ? p
* transitions. Whereas the
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stance a high intensity band in the region 224–230 nm, a medium
intensity band in the region 307–317 nm and a second medium
intensity low energy absorption band in the visible region 394–
437 nm. The medium intensity bands in the UV region is assigned
to
ter and intra-ligand
energy absorption band in the visible region is assigned to metal-
p–p
*, the high intensity band in the UV region is assigned to in-
*
p–p
*
/n–p
transitions [24,27], while the low
*
to-ligand charge transfer (MLCT) (t2g–p ).
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In this work, we have showed that ligand L reacts with arene
ruthenium and pentamethylcyclopentadienyl rhodium and iridium
complexes to yield a series of mono and dinuclear complexes in
good yield, which are remarkably stable in air as well as in solu-
*
tion. The Cp rhodium and iridium derivatives yielded both mono
and dinuclear complexes, while only dinuclear complexes are ob-
tained with the arene ruthenium analogues, despite different mo-
lar ratio of ligands. In all these, both mono and dinuclear
complexes the metal atom is bonded to the coordinated sites N1
and N3 or N4 and N6.
Acknowledgements
K.M. Rao gratefully acknowledges the Department of Science
and Technology, New Delhi, (Sanction Order No. SR/S1/IC-11/
2004) for financial support.
Appendix A. Supplementary Material
CCDC <757062>, <757063> and <757064> contains the supple-
mentary crystallographic data for this paper. These data can be ob-
tained free of charge from The Cambridge Crystallographic Data
Centre via www.ccdc.cam.ac.uk/data_request/cif. Supplementary