The difficulty of coordinating mutually trans phosphine and aryl ligands in palladium complexes and its relation to important coupling processes. Syntheses and crystal structures of a family of palladium phosphino, triflato, perchlorato, and aquo-2-(arylazo)aryl complexes

Article abstract of DOI:10.1021/om961094h

The reaction between [Pd(C₆H₃N=NR-2, X-5)Cl]₂ and phosphines gives [Pd(C₆H₃N=NTo-2,Me-5)Cl(L)] [To = C₆H₄Me-4, L = PEt₃ (1a), PPh₂Me (1b)] or trans-[Pd(C₆H₃N₂To-2,Me-5)ClL₂] (L = PEt₃ (2a), PPh₂Me (2b), L₂ = bis(diphenylphosphino)methane = dppm (2c)) or trans-[Pd(C₆H₃N₂X-2, R-5)Cl(μ-dppm)]₂ (X = Me, R = To (3a); X - H, R = Ph (3b)), depending on the molar ratio of the reagents. Tl(QTf) (OTf = O₃SCF₃), AgClO₄, or AgSbF₆ react with 1a,b, 2a, 2c, or 3a to give, variously, [Pd(C₆H₃N=NTo-2,Me-5)(Y)(D] (L = PEt₃, Y = TfO (4a); L = PPh₂Me, Y = TfO (4b), ClO₄ (4b′), trans-[Pd(C₆H₃N₂To-2,Me-5)(OTf)(PEt ₃)₂] (5), [Pd(C₆H₃N₂To-2,Me-5)(η ¹-dppm)(η²-dppm)]Tfo (6), or [Pd(C₆H₃N=NR-2,X-5)(η²-dppm)]Y (X = Me, R = To, Y = TfO (7a)). Complexes [Pd(C⁶H³N=NR-2,X-5)(η²-dppm)]SbF ₆ (X = Me, R = To (7a′); X = H, R = Ph (7b)) can be prepared by reacting [Pd(C₆H₃N=NR-2,X-5)Cl]₂ with AgSbF₆ and dppm. Complex 4b′ reacts with PPh₂Me to give [Pd(C₆H₃N₂To-2,Me-5)(PPh₂Me) ₃]ClO₄ (8). Attempts to obtain single crystals of 4a, [Pd(C₆H₃N=NR-2,X-5)(PPh₃)(Me ₂CO)]ClO₄, or 7b lead to different products. From 4, an insertion into the Pd-OTf bond of one molecule of water gives [Pd(C₆H₃N=NTo-2,Me-5(OH₂-OTf)(PEt₃)] (9) while substitution of the acetone molecule by two water molecules occurs in the second case to give [Pd(C₆H₃N=NTo-2,Me-5){(μ₃-OH ₂)(?OClO₃)(OH₂)}(PPh₃)] (10). Finally, ready oxidation in the air of 7b gives [Pd(C₆H₄N=NPh-2)(η²-dppmO)]SbF₆ (11) [dppmO = bis(diphenylphosphino)methane monoxide]. [Pt(PPh₃)₃] reacts with [Hg(C₆H₃N₂To-2, Me-5)Cl] to give trans-tPt(C₆H₃N₂To-2,Me-5)Cl(PPh ₃)₂] (12), which in turn reacts with Tl(OTf) to give [Pt(C₆H₃N=NTo2,Me-5)(PPh₃)₂]TfO (13). Crystal structures of 2c·-1/2CH₂Cl₂, 4b′, 5, 6, 7a, 9, 10, and 11·2MeOH have been determined.

Full text of DOI:10.1021/om961094h

Organometallics 1997, 16, 2127-2138
2127
Th e Difficu lty of Coor d in a tin g Mu tu a lly tr a n s P h osp h in e
a n d Ar yl Liga n d s in P a lla d iu m Com p lexes a n d Its
Rela tion to Im p or ta n t Cou p lin g P r ocesses. Syn th eses
a n d Cr ysta l Str u ctu r es of a F a m ily of P a lla d iu m
P h osp h in o, Tr ifla to, P er ch lor a to, a n d
Aqu o-2-(a r yla zo)a r yl Com p lexes
J ose´ Vicente,*,† Aurelia Arcas, and Delia Bautista
Grupo de Quı´mica Organometa´lica,‡ Departamento de Quı´mica Inorga´nica, Facultad de
Quı´mica, Universidad de Murcia, Aptdo. 4021, E-30071 Murcia, Spain
Peter G. J ones*,§
Institut fu¨r Anorganische und Analytische Chemie, Technische Universita¨t Braunschweig,
Postfach 3329, 38023 Braunschweig, Germany
Received December 26, 1996X
The reaction between [Pd(C6H3NdNR-2, X-5)Cl]2 and phosphines gives [Pd(C6H3NdNTo-
2,Me-5)Cl(L)] [To ) C6H4Me-4, L ) PEt3 (1a ), PPh2Me (1b)] or trans-[Pd(C6H3N2To-2,Me-
5)ClL2] (L ) PEt3 (2a ), PPh2Me (2b), L2 ) bis(diphenylphosphino)methane ) dppm (2c)) or
trans-[Pd(C6H3N2X-2, R-5)Cl(µ-dppm)]2 (X ) Me, R ) To (3a ); X ) H, R ) Ph (3b)), depending
on the molar ratio of the reagents. Tl(OTf) (OTf ) O3SCF3), AgClO4, or AgSbF6 react with
1a ,b, 2a , 2c, or 3a to give, variously, [Pd(C6H3NdNTo-2,Me-5)(Y)(L)] (L ) PEt3, Y ) TfO
(4a ); L ) PPh2Me, Y ) TfO (4b), ClO4 (4b′)), trans-[Pd(C6H3N2To-2,Me-5)(OTf)(PEt3)2] (5),
[Pd(C6H3N2To-2,Me-5)(η1-dppm)(η2-dppm)]TfO (6), or [Pd(C6H3NdNR-2,X-5)(η2-dppm)]Y (X
) Me, R ) To, Y ) TfO (7a )). Complexes [Pd(C6H3NdNR-2,X-5)(η2-dppm)]SbF6 (X ) Me, R
) To (7a ′); X ) H, R ) Ph (7b)) can be prepared by reacting [Pd(C6H3NdNR-2,X-5)Cl]2 with
AgSbF6 and dppm. Complex 4b′ reacts with PPh2Me to give [Pd(C6H3N2To-2,Me-5)(PPh2-
Me)3]ClO4 (8). Attempts to obtain single crystals of 4a , [Pd(C6H3NdNR-2,X-5)(PPh3)(Me2-
CO)]ClO4, or 7b lead to different products. From 4, an insertion into the Pd-OTf bond of
one molecule of water gives [Pd(C6H3NdNTo-2,Me-5(OH2‚‚‚OTf)(PEt3)] (9) while substitution
of the acetone molecule by two water molecules occurs in the second case to give
[Pd(C6H3NdNTo-2,Me-5){(µ3-OH2)(‚‚‚OClO3)(‚‚‚OH2)}(PPh3)] (10). Finally, ready oxidation
in the air of 7b gives [Pd(C6H4NdNPh-2)(η2-dppmO)]SbF6 (11) [dppmO ) bis(diphenylphos-
phino)methane monoxide]. [Pt(PPh3)3] reacts with [Hg(C6H3N2To-2, Me-5)Cl] to give trans-
[Pt(C6H3N2To-2,Me-5)Cl(PPh3)2] (12), which in turn reacts with Tl(OTf) to give [Pt(C6H3NdNTo-
2,Me-5)(PPh3)2]TfO (13). Crystal structures of 2c‚1/2CH2Cl2, 4b′, 5, 6, 7a , 9, 10, and
11‚2MeOH have been determined.
In tr od u ction
cis-[Au(C6H3NdNR-2,X-5)(R′)Cl] (X ) Me, H; R ) To,
Ph; R′ ) C6F5, C6H4NO2-2, C6H4N2Ph, CH2C(O)Me)
react with PPh3 to give the corresponding coupling
products and [AuCl(PPh3)] (Scheme 1).2
Arylpalladium complexes with phosphines are inter-
mediates in useful catalytic organic reactions. Thus,
trans-[Pd(Ar)X(PR3)2] (Ar ) aryl) complexes (obtained,
for example, by oxidative addition of ArX to [Pd(PR3)n])
react with organometallic derivatives of main group
elements R-[M] (R ) alkyl, aryl, alkenyl, allyl, benzyl
and M ) Li, Mg, Cu, Zn, B, Al, Sn) to give the coupling
product Ar-R (Scheme 1).1 We have extended the
observation to gold(III) systems. Thus, the complexes
We have recently observed that all attempts to
prepare [Pd(C6H3NdNR-2,X-5)(PPh3)2]+ (X ) Me, H; R
) To, Ph) were unsuccessful (Scheme 2).3 Thus, by
(1) Tsuji, J . Palladium Reagents and Catalysts. Innovation in
Organic Synthesis. J ohn Wiley: New York, 1995. Heck R. F. Palladium
Reagents in Organic Synthesis; Academic Press: New York, 1985.
(2) (a) Vicente, J .; Bermu´dez, M. D.; Escribano, J . Organometallics
1991, 10, 3380. (b) Vicente, J .; Bermu´dez, M. D.; Carrio´n, F. J . Inorg.
Chim. Acta 1994, 220, 1.
† jvs@fcu.um.es.
‡ http://www.scc.um.es/gi/gqo/.
§ jones@xray36.anchem.nat.tu-bs.de.
X Abstract published in Advance ACS Abstracts, April 15, 1997.
S0276-7333(96)01094-1 CCC: $14.00 © 1997 American Chemical Society

2128 Organometallics, Vol. 16, No. 10, 1997
Sch em e 1. Exa m p les of C-C Cou p lin ga
Vicente et al.
Sch em e 2. Exa m p les of C-P a n d C-N Cou p lin gsa
a
The dashed arrows indicate postulated processes. The
mutually trans aryl and phosphine ligands are indicated by
||| and the coupling processes by fr.
reacting [Pd(C6H3NdNR-2,X-5)(acac)] (acac ) acetylac-
etonate) with aqueous HClO4 and PPh3 in acetone, the
complex [Pd(C6H3NdNR-2,X-5)(PPh3)(acetone)]ClO4 was
isolated, even using a Ph3P to Pd ratio of 2:1. If the
reaction is attempted in dichloromethane, the C-P
coupling product, phosphonium salt [Ph3P(C6H3N2R-
2,X-5)]+, was obtained instead.
There are many other examples of coupling reactions
when a phosphine is forced to be coordinated trans to
an organic group. Thus, C-P coupling products allyl-
triphenylphosphonium salts form when complexes [Pd-
(η3-allyl)(PPh3)2]+ react with excess of PPh3.4a Simi-
larly, C-N coupling products are obtained when excess
of PPh3 is added to [Pd(η3-allyl)(µ-Cl)]2, where the allyl
group has a pyridyl substituent.4b Addition of PPh3 to
C,N-palladacyclic complexes leads to C-N coupling
products.5 Improved catalytic systems for the synthesis
of secondary amines from aryl halides and primary
amines have recently been developed using palladium
complexes with some special phosphines (Scheme 2).6
a
The dashed arrows indicate postulated processes. The
mutually trans aryl and phosphine ligands are indicated by
||| and the coupling processes by fr.
is considerable interest in this type of palladium com-
plexes, mainly associated with the high activity and
selectivity that they show in several important reac-
tions, such as the dimerization of methyl acrylates7 and
CO-olefin copolymerization.8
In the course of this work, we have also found that,
in contrast to phosphorus donor ligands, coordination
of weak O-donor ligands, such as triflato, perchlorato,
or aquo, trans to an aryl ligand is relatively easy. There
Exp er im en ta l Section
C, H, N, and S analyses, melting point measurements,
infrared and NMR spectra, and purification of solvents were
carried out as described previously.9 Pt(PPh3)3,10 [Hg(C6H3N2-
(3) Vicente, J .; Arcas, A.; Bautista, D.; Tiripicchio, A.; Tiripicchio-
Camellini, M. New J . Chem. 1996, 20, 345.
(4) (a) Malet, R.; Moreno-Man˜as, M.; Pleixats, R. Organometallics
1994, 13, 397 and references therein. (b) Chengebroyen, J .; Pfeffer,
M.; Sirlin, C. Tetrahedron Lett. 1996, 37, 7263.
(5) Pfeffer, M.; Sutter, J .-P.; Rotteveel, M. A.; De Cian, A.; Fischer,
J .; Tetrahedron 1992, 48, 2427. Pfeffer, M.; Sutter, J .-P.; De Cian, A.;
Fischer, J . Organometallics 1992, 12, 1167.
(6) Wolfe, J . P.; Wagaw, S.; Buchwald, S. L. J . Am. Chem. Soc. 1996,
118, 7215. Driver, M. S.; Hartwig, J . F. J . Am. Chem. Soc. 1996, 118,
7217.
To-2, Me-5)Cl],11 and [Pd(C6H3NdNR-2, X-5)Cl]2 (R ) H, Me;
(7) See for example: Oeheme, G.; Pracejus, H. J . Organomet. Chem.
1987, 320, C56.
(8) See for example: van Aseelt, R.; Gielens, E. E. C. G.; Rulke, R.
E.; Vrieze, K; Elsevier, C. J . J . Am. Chem. Soc. 1994, 116, 977.
(9) Vicente, J .; Abad, J . A.; Gil-Rubio, J . Organometallics 1996, 15,
3509.
(10) Ugo, R.; Cariati, F.; La Monica, G. Inorg. Synth. 1968, 11, 105.

Phosphine and Aryl Ligands in Palladium Complexes
Organometallics, Vol. 16, No. 10, 1997 2129
12.00 (s). Anal. Calcd for C26H43N2ClP2Pd: C, 53.15; H, 7.39;
N, 4.77. Found: C, 52.76; H, 7.43; N, 4.66.
Ch a r t 1
2b. Yield: 1260 mg, 87%. Mp: 146 °C. 1H NMR (300 MHz,
3
CDCl3, δ, ppm): 7.95 (d, 2 H, H22, H26, J HH ) 8.4 Hz), 7.6-7
(m, aromatic protons), 6.79 (s, 1 H, H16), 6.52 (d, 1 H, H14, 3J HH
) 8.1 Hz), 2.47 (s, 3 H, Me (azotolyl)), 1.89 (s, 3 H, Me
(azotolyl)), 1.63 (s, br, Me of PPh2Me). 31P{1H} NMR (121
MHz, CDCl3, δ, ppm): 6.67 (s). Anal. Calcd for C40H39N2ClP2-
Pd: C, 63.92; H, 5.24; N, 3.77. Found: C, 64.00; H, 5.26; N,
3.60.
2c. Yield: 620 mg, 95%. Mp: 144 °C. 1H NMR (300 MHz,
CDCl3, -60 °C, δ, ppm): 7.84-6.43 (m, aromatic protons), 4.5-
2.7 and 2.4-2.1 (m, CH2 (dppm)), 2.516, 1.591 (Me (azotolyl),
2c), 2.525, 2.002 (Me, [Pd(C6H3N2To-2, Me-5)(η1-dppm)(η2-
dppm)]Cl), 2.495, 1.838 (Me (azotolyl), 3a ). 31P{1H} NMR (121
MHz, CDCl3, -60 °C, δ, ppm) (Chart 2). 2c: 13.53 and -29.36
(“t” of an AA′XX′ system, | J AX + 4J AX′| ) 39 Hz). [Pd(C6H3N2-
2
2
To-2, Me-5)(η1-dppm)(η2-dppm)]Cl: 11.16 (ddd, PA, J AM
)
X ) Ph, To)12 were prepared following reported procedures.
Reactions were carried without precautions to exclude atmo-
spheric moisture (except for 1a , 2a ) and at room temperature
unless otherwise stated. Chart 1 shows the atom numbering
of the azoaryl groups used in the assignment of NMR reso-
nances.
2
2
351.6 Hz, J AQ ) 51.2 Hz, J AX ) 26.6 Hz), -25.44 (dd, PM,
2J MX ) 69.2 Hz), -32.62 (d, PQ), -33.79 (dd, PX). 3a : 6.63 (s).
dppm: -25.90. Anal. Calcd for C64H57N2P4Pd: C, 68.51; H,
5.15; N, 2.53. Found: C, 68.63; H, 5.14; N, 2.50. Single
crystals of 2c were obtained by slow diffusion of n-hexane into
a solution of 2c in dichloromethane.
Syn th esis of [P d (C6H3NdNTo-2,Me-5)Cl(L)] (L ) P Et3
(1a ), P P h 2Me (1b)), tr a n s-[P d (C6H3N2To-2,Me-5)Cl(L)2] (L
) P Et3 (2a ), P P h 2Me (2b), L2 ) Bis(d ip h en ylp h osp h in o)-
m eth a n e ) d p p m (2c)) a n d tr a n s-[P d (C6H3N2X-2,R-5)Cl-
(µ-d p p m )]2 (X ) Me, R ) To (3a ); X ) H, R ) P h (3b)). To
3a . Yield: 564 mg, 87%. Mp: 157 °C. 1H NMR (300 MHz,
CDCl3, δ, ppm): 7.54-6.58 (m, aromatic protons), 4.11-3.60
(dm, 2 H, CH2 (dppm)), 2.48 (s, 3 H, Me (azotolyl)), 1.95 (s, 3
H, Me (azotolyl)), 1.27 (m, CH2 n-hexane), 0.88 (t, Me n-hexane,
3J HH ) 7.2 Hz). 31P{1H} NMR (121 MHz, CDCl3, δ, ppm): 6.68.
Anal. Calcd for C78H70Cl2N4P4Pd2‚0.17n-hexane: C, 63.87; H,
4.91; N, 3.77. Found: C, 64.04; H, 4.81; N, 3.81.
a suspension of [Pd(C6H3NdNTo-2,Me-5)Cl]2 (To ) C6H4Me-
4) or [Pd(C6H4NdNPh-2)Cl]2 in dichloromethane (1a , 2a ,c,
3a ,b) or acetone (1b, 2b), the corresponding ligand (L:Pd )
0.9 (1a ), 1 (1b, 3a ,b), 2 (2a ,b,c)) was added. The solution was
stirred for 5 (1a ), 10 (2b, 3a ), and 15 (2a ) min or 2 (1b, 3b) or
3 (2c) h. Complex 1b was obtained by filtration of the
resulting suspension. Complexes 1a , 2c, and 3a were isolated
by concentration of the resulting solution (2-3 mL) and
addition of n-hexane (15-20 mL), and complexes 2a ,b, and
3b were obtained by evaporation of the solvent and washing
the solid with n-hexane. Color: yellow (1a ,b), orange (2a ),
orange-red (3a ), orange-yellow (3b), purple (2b,c).
3b. Yield: 366 mg, 95%. Mp: 188 °C. 1H NMR (300 MHz,
CDCl3, δ, ppm): 7.64-6.75 (m, aromatic protons), 3.99-3.91
(m, 2H, CH2 of dppm). 31P{1H} NMR (121 MHz, CDCl3, δ,
ppm): 5.88. Anal. Calcd for C74H62Cl2N4P4Pd2: C, 62.81; H,
4.42; N, 3.96. Found: C, 62.57; H, 4.64; N, 4.33.
Syn th esis of [P d (C6H3NdNTo-2,Me-5)(X)(L)] (X ) OTf
(OTf ) CF 3SO3), L ) P Et3 (4a ), P P h 2Me (4b); X ) ClO4, L
) P P h 2Me (4b′)), tr a n s-[P d(C6H3N2To-2,Me-5)(OTf)(P Et3)2]
(5), [P d (C6H3N2To-2,Me-5)(η1-d p p m )(η2-d p p m )]TfO (6),
[P d (C6H3NdNTo-2,Me-5)(η2-d p p m )]OTf (7a ). To a solution
of the corresponding chloro complex in acetone (10-15 mL),
Tl(OTf) or AgClO4 was added (molar ratio X:Pd ) 1). The
resulting suspension was stirred for 30 (4a , 5) min or 1 (4b′,
7a ) or 2 (4b, 6) h. The solvent was evaporated, and the residue
was extracted with dichloromethane (10 mL) and then filtered
through Celite. The resulting solution was concentrated (2
mL), and addition of n-hexane (10-15 mL, 4a ,b) or diethyl
ether (25 mL, 7a ) precipitated the complexes. Alternatively,
the solution was concentrated to dryness and the solid washed
with diethyl ether to give 4b′, 5, 6. Color: yellow (4a ,b,b′,
7a ), red (5), orange (6).
1a . Yield: 197 mg, 70%. Mp: 107 °C. IR: ν(Pd-Cl) 290
cm-1
.
1H NMR (300 MHz, CDCl3, δ, ppm): 7.90 (d, 1 H, H13
,
3
3J HH ) 7.8 Hz), 7.78 (d, 2 H, H22, H26, J HH ) 8.1 Hz), 7.24 (d,
2 H, H23, H25, 3J HH ) 9.3 Hz), 7.08 (d, 1 H, H14, 3J HH ) 6.3 Hz),
4
7.06 (d, 1 H, H16, J PH ) 4.5 Hz), 2.40 (s, 6 H, Me (azotolyl)),
3
2
2.10 (dq, 8 H, CH2, J HH ) 7.5 Hz, J HP ) 8.1 Hz), 1.22 (dt, 9
H, Me (PEt3), J HP ) 17.4 Hz). 31P{1H} NMR (121 MHz,
3
CDCl3, δ, ppm): 31.34 (s). Anal. Calcd for C20H28N2ClPPd:
C, 51.18; H, 6.026; N, 5.97. Found: C, 51.35; H, 6.11; N, 5.77.
1b. Yield: 558 mg, 81%. Mp: 197 °C (dec). IR: ν(Pd-Cl)
288 cm-1
22, H26
7.8-7.4 (m, aromatic protons of PPh2Me), 7.25 (d, 2 H, H23
.
1H NMR (300 MHz, CDCl3, δ, ppm): 7.83 (d, 2 H,
H
,
3J HH ) 8.4 Hz), 7.82 (d, 1 H, H13
,
3J HH ) 7.8 Hz),
4a . Yield: 210.0 mg, 87%. Mp: 149 °C. 1H NMR (300
,
)
3
3
4
3
H25, J HH ) 8.4 Hz), 6.87 (dd, 1 H, H14, J HH ) 7.9 Hz, J HH
MHz, CDCl3, δ, ppm): 7.86 (d, 1 H, H13, J HH ) 7.8 Hz), 7.70
0.9 Hz), 6.06 (dd, 1 H, H16, 4J HP ) 8.1 Hz, 4J HH ) 0.9 Hz), 2.41
(d, 2 H, H22, H26, 3J HH ) 8.4 Hz), 7.23 (d, 2 H, H23, H25, 3J HH
)
2
8.4 Hz), 7.10 (d, 1 H, H14
, ,
3J HH ) 7.5 Hz), 6.91 (d, 1 H, H16
(s, 3 H, Me (azotolyl)), 2.29 (d, 3 H, Me (PPh2Me), J HP ) 10.8
Hz), 1.81 (s, 3 H, Me (azotolyl)). 31P{1H} NMR (121 MHz,
CDCl3, δ, ppm): 25.01 (s). Anal. Calcd for C27H26N2ClPPd:
C, 58.81; H, 4.76; N, 5.08. Found: C, 58.78; H, 4.65; N, 5.18.
2a . Yield: 607 mg, 84%. Mp: 130 °C. IR: ν(Pd-Cl) 304
4J PH ) 6.0 Hz), 2.40 (s, 3 H, Me (azotolyl)), 2.37 (s, 3 H, Me
2
3
(azotolyl)), 2.08 (dq, 6 H, CH2 (PEt3), J PH ) 7.5 Hz, J HH
)
3
3
7.5 Hz), 1.24 (dt, 9 H, Me (PEt3), J HH ) 7.8 Hz, J PH ) 17.4
Hz). 31P{1H} NMR (121 CDCl3, δ, ppm): 32.09 (s). Anal. Calcd
for C21H28F3N2O3PPdS: C, 43.26; H, 4.85; N, 4.81; S, 5.50.
Found: C, 43.77; H, 4.95; N, 4.91; S, 5.56.
cm-1
.
1H NMR (300 MHz, CDCl3, δ, ppm): 7.96 (d, 2 H, H22
,
3
3
H
26, J HH ) 8.4 Hz), 7.5 (d, 1 H, H13, J HH ) 8.1 Hz), 7.39 (s, 1
H, H16), 7.27 (d, 2 H, H23, H25,
3J HH ) 8.1 Hz), 6.83 (d, 1 H,
4b. Yield: 91 mg, 74%. Mp: 144 °C. 1H NMR (300 MHz,
3
H
14, J HH ) 7.5 Hz), 2.41 (s, 3 H, Me (azotolyl)), 2.32 (s, 3H,
CDCl3, δ, ppm): 7.83-7.26 (m, 15 H, aromatic protons), 6.92
Me (azotolyl)), 1.48 (m, 12 H, CH2), 0.98 (apparent quintuplet,
3
4
(d, 1 H, H14, J HH ) 7.2 Hz), 6.21 (d, 1 H, H16, J HP ) 9.3 Hz),
18 H, Me (PEt3)). 31P{1H} NMR (121 MHz, CDCl3, δ, ppm):
2
2.42 (s, 3 H, Me (azotolyl)), 2.21 (d, 3 H, Me of PPh2Me, J HP
) 11.1 Hz), 1.87 (s, 3 H, Me (azotolyl)). 31P{1H} NMR (121
(11) Roling, P. V.; Kirt, D. D.;Dill, J . L.; Hall, S.; Holstrom, C. J .
Organomet. Chem. 1976, 39, 116.
(12) Cope, A. C.; Siekman, R. W. J . Am. Chem. Soc. 1965, 87, 3272.
Siedle, A. R. J . Organomet. Chem. 1981, 208, 115.
MHz, CDCl3, δ, ppm): 25.30 (s). Anal. Calcd for C28H26
-
F3N2O3PPdS: C, 50.57; H, 3.95; N, 4.22; S, 4.82. Found: C,
50.70; H, 4.03; N, 4.18; S, 4.58.

2130 Organometallics, Vol. 16, No. 10, 1997
Vicente et al.
Ch a r t 2
4b′. Yield: 288 mg, 85%. Mp: 173 °C. IR: νsym(Cl-O)
1168, 1148, 1128, 1104 cm-1; νasym(Cl-O) 618, 608 cm-1 1H
NMR (300 MHz, CDCl3, δ, ppm): 8.1-7.30 (m, 15 H, aromatic
Me(dmpap)). 31P{1H} NMR (121 MHz, CDCl3, δ, ppm): -4.76
(d, 2J PP ) 67.27 Hz), -30.06 (d, 2J PP ) 67.39 Hz). Anal. Calcd
for C39H35F6N2P2PdSb: C, 50.05; H, 3.78; N, 2.99. Found: C,
50.14; H, 3.75; N, 2.94.
.
3
protons), 6.94 (d, 1 H, H14, J HH ) 7.8 Hz), 6.20 (d, 1 H, H16
,
4J HP ) 7.8 Hz), 2.42 (s, 3 H, Me (azotolyl)), 2.21 (d, 3 H, Me of
7b. Yield: 250 mg, 69%. Mp: 226 °C (dec). 1H NMR (300
MHz, CDCl3, δ, ppm): 8.12-6.75 (m, aromatic protons), 4.34
(dd, CH2 of dppm, 2J PH ) 11.4 and 8.7 Hz). 31P{1H} NMR (121
PPh2Me, 2J PH ) 11.1 Hz), 1.86 (s, 3 H, Me (azotolyl)). 31P{1H}
NMR (121 MHz, CDCl3, δ): 25.91 (s). Anal. Calcd for C27H26
-
2
ClN2O4PPd: C, 52.69; H, 4.27; N, 4.55. Found: C, 52.64;
H,4.24; N, 4.36. Single crystals of 4b′ were obtained by slow
diffusion of diethyl ether into a solution of 4b′ in dichlo-
romethane.
MHz, CDCl3, δ, ppm): -6.72 (d, J PP ) 69.57 Hz), -32.43 (d,
2J PP ) 68.24 Hz). Anal. Calcd for C37H31F6N2P2PdSb: C,
48.96; H, 3.44; N, 3.09. Found: C, 49.04; H, 3.29; N, 3.03.
Syn th esis of [P d (C6H3N2To-2,Me-5)(P P h 2Me)3]ClO4 (8).
To a solution of 4b′ (209 mg, 0.34 mmol) in chloroform (6 mL)
was added PPh2Me (128 µL, 0.68 mmol). The solution was
stirred for 2 h and then concentrated to dryness. Addition of
diethyl ether (10 mL) and vigorous stirring for 20 min gave 8
as an orange solid. Yield: 300 mg, 87%. Mp: 116 °C. IR:
5. Yield: 228 mg, 73%. Mp: 108 °C. 1H NMR (300 MHz,
CDCl3, δ, ppm): 8.01 (d, 2 H, H22, H26, 3J HH ) 8.4 Hz), 7.57 (d,
1 H, H13, 3J HH ) 8.1 Hz), 7.33 (d, 2 H, H23, H25, 3J HH ) 8.1 Hz),
3
7.31 (s, 1 H, H16), 6.90 (d, 1 H, H14, J HH ) 8.1 Hz), 2.43 (s, 3
H, Me (azotolyl)), 2.34 (s, 3 H, Me (azotolyl)), 1.43 (m, 12 H,
CH2 (PEt3)), 0.98 (apparent quintuplet, 18 H, Me (PEt3)). 31P-
{1H} NMR (121 MHz, CDCl3, δ, ppm): 10.91 (s). Anal. Calcd
for C27H43F3N2O3P2PdS: C, 46.23; H, 6.19; N, 4.03; S, 4.57.
Found: C, 46.08; H, 6.48; N, 4.10; S, 4.48. Single crystals of
5 were obtained by slow diffusion of n-hexane into a solution
of 5 in diethyl ether.
ν(Cl-O) 1093 cm-1; ν(Cl-O) 623 cm-1
.
1H NMR (300 MHz,
CDCl3, δ, ppm): 7.90 (d, 2 H, H22, H26, 3J HH ) 8.1 Hz), 7.53 (d,
2 H, H23, H25, 3J HH ) 7.8 Hz), 7.46-6.80 (m, aromatic protons),
3
3
6.65 (d, 1 H, H13, J HH ) 6.9 Hz), 6.46 (s, 1 H, H14, J HH ) 8.1
Hz), 2.61 (s, 3 H, Me (azotolyl)), 1.79 (s, 3 H, Me (azotolyl)),
2
1.62 (d, 3 H, Me (PPh2Me), J PH ) 6.9 Hz), 1.37 (s, br, 6H, 2
6. Yield: 265 mg, 85%. Mp: 133 °C. 1H NMR (300 MHz,
CDCl3, δ, ppm): 7.68-6.90 (m, aromatic protons), 4.37 (m, br,
1 H, CH2 (dppm)), 4.1 (m, br, 1 H, CH2 (dppm)), 2.53 (s, 3 H,
Me (azotolyl)), 2.33 (m, br, 2 H, CH2 (dppm)), 2.00 (s, 3 H, Me
(azotolyl)). 31P{1H} NMR (121 MHz, CDCl3, δ, ppm, -60 °C)
Me of PPh2Me). 31P{1H} NMR (121 MHz, CDCl3, δ, ppm): 6.24
(d, 2J PP ) 36 Hz), -2.63 (t). Anal. Calcd for C53H52ClN2O4P3-
Pd: C, 62.66; H, 5.17; N, 2.76. Found: C, 61.67; H, 5.07; N,
2.71.
2
2
Syn th esis of [P d(C6H3NdNTo-2,Me-5)(OH2‚‚‚OTf)(P Et3)]
(9). Single crystals of 9 were obtained by slow diffusion of
n-pentane into a solution of 4a in dichloromethane. Mp: 171
(Chart 2): 11.68 (ddd, PA, J AM ) 353.4 Hz, J AQ ) 50.7 Hz,
2J AX ) 26.1 Hz), -24.85 (dd, PM, J MX ) 61.9 Hz), -32.52 (d,
2
PQ), -33.32 (dd, PX). Anal. Calcd for C65H57F3N2O3P4PdS: C,
63.28; H, 4.67; N, 2.27; S, 2.60. Found: C, 63.21; H, 4.73; N,
2.26; S, 2.89. Single crystals of 6 were obtained by slow
diffusion of n-hexane into a solution of 6 in dichloromethane.
7a . Yield: 178 mg, 76%. Mp: 206 °C. 1H NMR (300 MHz,
CDCl3, δ, ppm): 7.96-6.44 (m, aromatic protons), 4.47 (dd,
°C. 1H NMR (300 MHz, CDCl3, δ, ppm): 7.87 (d, 1 H, H13
,
3
3J HH ) 7.8 Hz), 7.67 (d, 2 H, H22, H26, J HH ) 8.4 Hz), 7.28 (d,
2 H, H23, H25, 3J HH ) 8.4 Hz), 7.11 (d, 1 H, H14, 3J HH ) 7.8 Hz),
4
6.87 (d, 1 H, H16, J PH ) 6.1 Hz), 2.76 (s, H2O), 2.41 (s, 3 H,
Me (azotolyl)), 2.40 (s, 3 H, Me (azotolyl)), 2.05 (dq, 6 H, CH2
(PEt3), 2J PH ) 9.9 Hz, 3J HH ) 7.5 Hz), 1.25 (dt, 9 H, Me (PEt3),
2
CH2 of dppm, J PH ) 11.8 and 8.3 Hz), 2.29 (s, 3 H, Me
3
3J HH ) 7.5 Hz, J PH ) 17.7 Hz). 31P{1H} NMR (121 CDCl3, δ,
(azotolyl)), 2.01 (s, 3 H, Me (azotolyl)). 31P{1H} NMR (121
,
2J PP ) 67.7 Hz),
ppm): 21.65 (s). Anal. Calcd for C21H30F3N2O4PPdS: C, 41.95;
H, 5.04; N, 4.70; S, 5.33. Found: C, 41.85; H, 5.05; N, 4.69; S,
5.37.
MHz, CDCl3, δ, ppm): -5.35 (d, Ptrans
to N
-30.60 (d, Ptrans to C). Anal. Calcd for C40H35F3N2O3P2PdS: C,
56.57; H, 4.16; N, 3.30; S, 3.77. Found: C, 56.92; H, 4.23; N,
3.23; S, 3.60.
Syn th esis of [P d (C6H3NdNTo-2,Me-5){(µ3-OH2)(‚‚‚OCl-
O3)(‚‚‚OH2)}(P P h 3)] (10). Single crystals of this compound
were obtained by slow diffusion of n-hexane into a solution of
[Pd(C6H3N2To-2,Me-5)(PPh3)(acetone)]ClO4 in dichloromethane.3
1H NMR (300 MHz, CDCl3, δ, ppm): 7.75-7.26 (m, aromatic
Syn th esis of [P d (C6H3NdNTo-2,Me-5)(η2-d p p m )]SbF 6
(7a ′) a n d [P d (C6H4NdNP h -2)(η2-d p p m )]SbF 6 (7b). To a
solution of [Pd(C6H3NdNTo-2,Me-5)Cl]2 or [Pd(C6H4NdNPh-
2)Cl]2 in acetone (20 mL) was added AgSbF6 (molar ratio Pd:
Ag ) 1). The resulting suspension was refluxed for 30 min.
The AgCl formed was removed by filtration thorough Celite,
and dppm (molar ratio Pd:dppm ) 1) was added to the
resulting solution. The solution was stirred at room temper-
ature for 1 h, evaporated almost to dryness, and diethyl ether
(20 mL) was added to give 7a ′ or 7b as an orange solid.
7a ′. Yield: 230 mg, 60%. Mp: 223 °C. 1H NMR (300 MHz,
CDCl3, δ, ppm): 7.94 (dd, H13, 3J HH ) 7.5 Hz, 5J PH ) 3.60 Hz),
7.79-7.72 (m, aromatic protons), 7.59-7.31 (m, aromatic
3
3
protons), 6.93 (d, H14, J HH ) 7.8 Hz), 6.16 (d, H16, J HP ) 7.8
Hz), 2.405 (s, 3 H, Me(azotolyl)), 1.78 (s, 4 H, H2O), 1.76 (s, 3
H, Me(dmpap)). 31P{1H} NMR (121 MHz, CDCl3, δ, ppm):
41.47. Anal. Calcd for C32H32ClN2O6PPd: C, 53.87; H, 4.53;
N, 3.93. Found: C, 53.81; H, 4.35; N, 3.84.
Syn th esis of [P d (C6H4NdNP h -2)(η2-d p p m O)]SbF 6 (11).
To a suspension of [Pd(C6H4NdNPh-2)(µ-Cl)]2 (73 mg, 0.113
mmol) in acetone (10 mL) was added AgSbF6 (78 mg, 0.227
mmol). The resulting suspension was refluxed for 1 h and then
concentrated to dryness; dichloromethane (20 mL) was added,
and the suspension was filtered thorough Celite. The ligand
dppmO was added to the resulting solution, the mixture stirred
protons), 7.09 (d, H14, 3J HH ) 7.8 Hz), 6.93 (d, H23, H25, 3J HH
)
8.4 Hz), 6.46 (t, H16, 4J PH ) 9 Hz), 4.35 (dd, CH2 of dppm, 2J PH
) 11.4 and 8.1 Hz), 2.30 (s, 3 H, Me(azotolyl)), 2.01 (s, 3 H,

Phosphine and Aryl Ligands in Palladium Complexes
Organometallics, Vol. 16, No. 10, 1997 2131
for 1 h, and then was concentrated to 2 mL. Addition of diethyl
ether (25 mL) gave 11 as a yellow solid. Yield: 100 mg, 96%.
Mp: 230 °C. 1H NMR (300 MHz, CDCl3, δ, ppm): 8.37-6.45
(m, aromatic protons), 3.86 (dd, CH2, 2J PH ) 12.00 and 9.9 Hz).
31P{1H} NMR (121 MHz, CDCl3, δ, ppm): 55.56 (d, 2J PP ) 16.0
Hz), 32.30 (d). Anal. Calcd for C37H31F6N2OP2PdSb: C, 48.10;
H, 3.39; N, 3.03. Found: C, 48.14; H, 3.35; N, 2.64. Single
crystals of 11 were obtained from MeOH.
Resu lts
Scheme 3 presents our reaction sequences. In some
cases, salts with different anions were prepared in order
to obtain crystals suitable for X-ray structure analysis.
Our interest in obtaining useful intermediates for
preparing complexes with a phosphine ligand trans to
the aryl group prompted us to isolate interesting
complexes with weak donor ligands, such as triflato and
perchlorato, and new types of aquo complexes of pal-
Syn th esis of tr a n s-[P t(C6H3N2To-2,Me-5)Cl(P P h 3)2] (12).
To a suspension of [Pt(PPh3)3] (277 mg, 0.282 mmol) in toluene
(20 mL) was added [Hg(C6H3N2To-2,Me-5)Cl] (126 mg, 0.283
mmol). The resulting suspension was refluxed for 15 min and
then concentrated to dryness; the residue was extracted with
dichloromethane (30 mL) and filtered thorough Celite to
remove Hg. The solution was concentrated to 1 mL. Addition
of diethyl ether (8 mL) gave a solid that was a mixture. The
mother liquor was concentrated to dryness; addition of diethyl
ether (4 mL) and n-pentane (8 mL) gave 12 as an orange solid.
Yield: 180 mg, 66%. Mp: 168 °C. 1H NMR (300 MHz, CDCl3,
δ, ppm): 7.67-6.4 (m, aromatic protons), 2.46 (s, 3 H, Me
(azotolyl)), 1.71 (s, 3 H, Me (azotolyl)). 31P{1H} NMR (121
MHz, CDCl3, δ, ppm): 25 °C, 23.54 (br); -60 °C, 23.30 (s, 1J Pt,P
) 1554.5 Hz). Anal. Calcd for C50H43ClN2P2Pt: C, 62.26; H,
4.50; N, 2.90. Found: C, 62.15; H, 4.46; N, 2.75.
ladium. Thus, the reaction of [Pd(C6H3NdNR-2,X-5)-
Cl]2, orthometalation products of azobenzene or azotol-
uene, with phosphines gives [Pd(C6H3NdNTo-2,Me-
5)Cl(L)] (To ) C6H4Me-4, L ) PEt3 (1a ), PPh2Me (1b))
when the reaction is carried out with a 1:2 molar ratio
or trans-[Pd(C6H3N2To-2,Me-5)ClL2] (L ) PEt3 (2a ),
PPh2Me (2b), bis(diphenylphosphino)methane ) dppm
(2c)) with a 1:4 molar ratio. Complexes of both types
have been previously reported.13 The reaction with
dppm in a 1:1 molar ratio gives trans-[Pd(C6H3N2X-2,R-
5)Cl(µ2-dppm)]2 (X ) Me, R ) To (3a ); X ) H, R ) Ph
(3b)). Complex 3b crystallizes with n-hexane, which
could not be removed. It is known that some dppm
complexes tend to occlude solvent molecules.14 The
reaction of 1a or 1b with Tl(OTf) (OTf ) O3SCF3) or 1b
Syn th esis of [P t(C6H3NdNTo-2,Me-5)(P P h 3)2]TfO (13).
To a solution of 12 (125 mg, 0.130 mmol) in acetone (10 mL)
was added Tl(OTf) (47 mg, 0.133 mmol). The resulting
suspension was stirred for 30 min. The suspension was
concentrated to dryness, and the residue was extracted with
dichloromethane (20 mL); the extract was filtered through
Celite and concentrated to 1 mL. Addition of diethyl ether (8
mL) gave 13 as an orange solid. Yield: 100 mg, 72%. Mp:
203 °C. 1H NMR (300 MHz, CDCl3, δ, ppm): 7.94-6.42 (m,
aromatic protons), 2.18 (s, 3 H, Me (azotolyl)), 1.82 (s, 3 H,
Me (azotolyl)). 31P{1H} NMR (121 MHz, CDCl3, δ, ppm): 19.46
with AgClO4 gives [Pd(C6H3NdNTo-2,Me-5)(Y)(L)] (L )
PEt3, Y ) TfO (4a ); L ) PPh2Me, Y ) TfO (4b), ClO4
(4b′)). Tl(OTf) reacts with 2a to give trans-[Pd(C6H3N2-
To-2, Me-5)(OTf)(PEt3)] (5), in which the weak donor
triflate anion is coordinated to palladium trans to the
aryl group, while it reacts with 2c or 3a to give [Pd-
(C6H3N2To-2,Me-5)(η1-dppm)(η2-dppm)]TfO (6) or [Pd-
2
1
2
(d, J PP ) 16.5 Hz, J PPt ) 2067 Hz), 15.03 (d, J PP ) 16.9 Hz,
1J PPt ) 3817 Hz). Anal. Calcd for C51H43F3N2O3P2PtS: C,
56.82; H, 4.03; N, 2.60; S, 2.97. Found: C, 56.86; H, 3.99; N,
2.560; S, 2.74.
(C6H3NdNTo-2,Me-5)(η2-dppm)]TfO (7a ), respectively.
The SbF6 salt analogous to 7a was prepared directly
starting from [Pd(C6H3NdNTo-2,Me-5)Cl]2; reaction
X-r ay Str u ctu r e Deter m in ation s. Crystals were mounted
in inert oil on glass fibers and transferred to the cold gas
stream of the diffractometer (Stoe STADI-4 for 4b′, 5, and 6,
otherwise Siemens P4, both with a Siemens LT-2 low-temper-
ature attachment). Data were collected using monochromated
Mo KR radiation in ω/θ (4b′, 5, 6), otherwise ω, mode. Cell
constants were refined from (ω angles (4b′, 5, 6) or setting
angles of ca. 50 reflections up to 2θ ) 23°. Absorption
corrections were applied for 2c and 10 with SHELXA (G. M.
Sheldrick, unpublished report) and for 5 and 9 on the basis of
ψ-scans. Structures were solved by direct methods (4b′),
otherwise by the heavy atom method, and refined anisotropi-
cally on F2 (program SHELXL-93, G. M. Sheldrick, University
of Go¨ttingen). Restraints to local aromatic ring symmetry or
light atom displacement factor components were applied in
some cases. Hydrogen atoms were included using rigid methyl
groups or a riding model. Full details are given in Table 1.
Particular features: 2c contains a dichloromethane molecule
badly disordered over an inversion center. One terminal ethyl
carbon (C32) of 5 is disordered over two positions. For 4b′,
the absolute structure was determined by an x refinement,
with x ) -0.06(2). In 6, the uncoordinated PPh2 group shows
significant residual electron density and may be slightly
disordered. The phenyl group C31-36 of compound 7 is
disordered over two positions, and the triflate anion is badly
resolved. The water H of compounds 9 and 10 were located
in difference syntheses and refined using distance restraints
(command SADI). Compound 11 crystallizes with two mol-
ecules of methanol, which are badly resolved and do not enter
into H bonding interactions.
with AgSbF6 (1:2) in acetone, removal of AgCl and
addition of dppm (Pd:dppm ) 1:1) gives [Pd(C6H3NdNTo-
2,Me-5)(η2-dppm)]SbF6 (7a ′). The complex [Pd(C6H4-
NdNPh-2)(η2-dppm)]SbF6 (7b) was obtained similarly.
The synthesis of complex [Pd(C6H4NdNPh-2)(η2-dppm)]-
ClO4 in a similar manner was already known.13c Com-
plex 2b reacts with AgClO4 to give a mixture of
[Pd(C6H3N2To-2,Me-5)(PPh2Me)3]ClO4 (8, see below)
and 4b. However, AgSbF6 reacts with 2c to give a 1:1
mixture of 3a and [Ag(dppm)]2(SbF6)2.
From 4b′, the perchlorato ligand is displaced by PPh2-
Me and the aryl chelate ring is opened to give [Pd-
(C6H3N2To-2, Me-5)(PPh2Me)3]ClO4 (8), which also con-
tains trans aryl and phosphine ligands. Attempts to
prepare the phosphonium salt [MePh2P(C6H3N2Me-2,-
To-5)]+ via C-P coupling3 by refluxing 8 in chloroform
(7 h) or [Et3P(C6H3N2Me-2,To-5)]+ by refluxing complex
5 with Et3P (1:1, 4 h) in chloroform failed because
(13) (a) Cross, R. J .; Tennent, N. H. J . Organomet. Chem. 1974, 72,
21. (b) Anderson, G. K.; Cross, R. J .; Leaman, S. A.; Robertson, F. J .;
Rycroft, D. S.; Rocamora, M. J . Organomet. Chem. 1990, 388, 221. (c)
Fornie´s, J .; Navarro, R.; Sicilia, V. Polyhedron 1988, 7, 2659. (d) Omae,
I. Organometallic Intramolecular-Coordination Compounds; Elsevi-
er: New York, 1986. (e) Weaver, D. L. Inorg. Chem. 1970, 10, 2250.
(14) Pringle, P. G.; Shaw, B. L. J . Chem. Soc., Dalton Trans. 1984,
849. Balch, A. L.; Benner, L. S.; Olmstead, M. M. Inorg. Chem. 1979,
18, 2996.

2132 Organometallics, Vol. 16, No. 10, 1997
Vicente et al.

Phosphine and Aryl Ligands in Palladium Complexes
Organometallics, Vol. 16, No. 10, 1997 2133
Sch em e 3
Sch em e 4
metallic palladium was not observed. Instead, a mix-
ture that could not be separated or an intractable oil
was obtained.
Attempts to grow single crystals of 4a or [Pd-
(C6H3NdNTo-2,Me-5)(PPh3)(Me2CO)]ClO4 (Scheme 2)
or 7b in air led to various complexes. In the first case,
an insertion of one molecule of water into the Pd-OTf
bond occurs to give the complex [Pd(C6H3NdNTo-2,Me-
5)(OH2‚‚‚OTf)(PEt3)] (9). In the second case, the acetone
ligand is replaced by two molecules of water; one is
coordinated to palladium and, via hydrogen bonding,
bridges the other water molecule and the perchlorate
anion to give [Pd(C6H3NdNTo-2,Me-5){(µ3-OH2)-
(‚‚‚OClO3)(‚‚‚OH2)}(PPh3)] (10). Finally, aerial oxidation
of 7b takes place to give 11 containing dppm monoxide
(dppmO). This complex can also be obtained by reacting
yield.13a By treating 12 with Tl(OTf), the complex [Pt-
(C6H3NdNTo-2,Me-5)(PPh3)2]TfO (13) can be isolated.
We have previously reported that the related palladium
complex could not be isolated, and instead, the phos-
phonium salt [Ph3P(C6H3N2R-2,X-5)]+ was obtained.3
This phosphonium salt was not observed when 13 was
reacted with PPh3 (in the NMR tube). The observed
mixture of compounds gave 13 after removing the
solvent.
[Pd(C6H3NdNR-2,X-5)Cl]2 with AgSbF6 and dppmO.
The orthoplatination of azobenzene has been achieved
by reacting azobenzene with K2[PtCl4]12 or with PtCl2,13a
but in very low yields. The reaction between [Pt(PPh3)3]
and [Hg(C6H4N2Ph-2)Cl] was reported to give [Pt-
(C6H4NdNPh-2)Cl(PPh3)].15 However, by reacting [Pt-
(PPh3)3] and [Hg(C6H3N2To-2,Me-5)Cl], we obtain a
different type of product, trans-[Pt(C6H3N2To-2,Me-5)-
Cl(PPh3)2] (12) (Scheme 4). The synthesis of [Pt-
(C6H4N2Ph-2)Cl(PEt3)2] has been reported by treating
[Hg(C6H4N2Ph-2)2] with cis-[PtCl2(PEt3)2], but in low
Discu ssion
Str u ctu r es of Com p lexes. The crystal structures
of complexes 2c, 4b′, 5, 6, 7a , 9, 10, and 11 have been
solved. Complex 2c (Figure 1 and Table 2) shows both
dppm ligands acting as monocoordinate and in trans
positions. A short contact between N(2) and Pd (2.634-
(2) Å) is observed, which however does not significantly
(15) This product was reported in a review (Sokolov, V. I.; Reutov,
O. A. Coord. Chem. Rev. 1978, 27, 89), however, it was not obtained
in pure form and, consequently, was never published. Private com-
munication of V. I. Sokolov.

2134 Organometallics, Vol. 16, No. 10, 1997
Vicente et al.
In complex 4b′ (Figure 3 and Table 2), the expected
coordination of PPh2Me cis to the carbon atom is
observed, as is the monocoordination of the perchlorato
ligand. As far as we are aware, only two X-ray crystal
structures of perchlorato palladium(II) complexes have
been previously reported.20,21 Although both are neutral
aryl complexes and show the perchlorato ligand trans
to the aryl group, the Pd-O bonds (2.202(3)20 2.222(3)21
Å) are significantly longer than in 4b′ (2.186(2) Å). The
expected lengthening of the Cl-O bond involving the
coordinated oxygen atom (1.484(2) Å) with respect to
the other three ClO bonds (1.397(3)-1.420(3) Å) is
observed. The same feature is observed in one of the
reported structures (Cl-O(Pd) ) 1.474(3) and 1.471(3)
Å for the two independent molecules and Cl-O )
1.411(4)-1.430(4) Å).20 In the other structure, the
perchlorato ligand is disordered.21
F igu r e 1. Crystal structure of complex 2c.
Complex 6 (Figure 4 and Table 2) shows one chelating
and one monocoordinate dppm ligand, whereas complex
7a (Figure 5 and Table 3) shows both the azophenyl and
dppm ligands chelating. The strong trans influence of
the aryl ligand is shown by the longer Pd-Ptrans to aryl
distances (2.359(2) (6), 2.413(3) Å (7a )) than Pd-
Pcis to aryl (2.324(2) (6), 2.318(2) (6), 2.259(3) Å (7a )).
Crystal structures of arylpalladium complexes contain-
ing chelating diphosphines, and therefore with aryl and
phosphine ligands in trans positions, have been re-
ported.22 However, those of 6 and 7a are the first with
dppm. Most crystal structures of palladium(II) com-
plexes containing phosphines trans to a carbon donor
ligand are aryl complexes and also show Pd-Ptrans to aryl
distort the planar coordination around the metal atom
(mean deviation of five atoms from best plane 0.03Å).
A similar situation occurs in complex 5 (Figure 2 and
Table 2); however, the Pd-N(2) bond is shorter (2.576(4)
Å) and, correspondingly, the square planar coordination
of palladium is distorted to give two planes about the
axis C11,O1,Pd with an interplanar angle of 21° (cf. P1-
Pd-P2 163.66(6)°). Such weak interactions have been
observed in a few other palladium complexes; the range
of observed Pd‚‚‚N distances is 2.523(8)-2.805(5) Å.16
A genuinely trigonal bipyramidal Pd(II) complex shows
an axial Pd-N bond distance of 2.23(2) Å.17
As far as we are aware, only two crystal structures
of palladium(II) triflato complexes have been re-
ported.18,19 The Pd-O(1) bond distance in 5 (2.184(4)
Å) is intermediate between that in the only similar
distances (2.340(2)-2.403(2) Å) longer than Pd-Pcis
-
(2.223(2)-2.325(3) Å).16a,22a-f,23a-d In those com-
to aryl
plexes with two or three phosphorus donor atoms, the
difference ∆ ) (Pd-Ptrans to aryl) - (Pd-Pcis to aryl) de-
pends on the nature of the complex. Thus, in those
complexes of the form [Pd(aryl)P3]+ (including 6), ∆ is
in the range 0.035-0.06 Å16a,23d while in those of the
type cis-[Pd(aryl)P2(L)]+, where P2 is a chelating diphos-
phine ligand and L ) Cl, I, or a nitrogen donor ligand
(like 7a ),22a-f,23c ∆ is in the range 0.097-0.154 Å because
of smaller trans influence of L than phosphorus ligands.
The only exception to all the above observations is found
in the structure of [Pd(C6F5)(PPh3){(PPh2)2CPPh2}], in
which the Pd-Ptrans to aryl bond (2.329(3)Å) is shorter
than one of the two Pd-Pcis to aryl bonds (2.366(3) Å).22g
In addition, this last distance is longer than any other
Pd-Pcis to aryl bond length. Complex 6, similar to 5,
reported complex [Pd{C(dO)(CH2)2NEt2}(OTf)(NEt2H)]
(2.271(7) Å)19 and that in [Pd(OTf‚‚‚HOH‚‚‚OTf){1,3-bis-
(diphenylphosphino)propane}] (2.159(3) Å), where the
triflato ligand is hydrogen bonded to a coordinated water
molecule.18 This trend in bond lengths can be attributed
to the decrease in the trans influence in the series
(diethylamino)propionyl, azophenyl, and phosphine
ligands. As in reference 19, there are C-H‚‚‚O contacts
that may be described as hydrogen bonds: C43-
H43A‚‚‚O2 (0.5 + x, 1.5 - y, 1 - z), with C‚‚‚O 3.38 Å,
H‚‚‚O 2.51 Å and C-H‚‚‚O 146°, and C33-H33B‚‚‚O3
(-0.5 + x, 1.5 - y, 1 - z; 3.41, 2.44 Å, 168°). The S-O(1)
bond distance, 1.453(4) Å, is significantly longer than
the other two bond lengths between the sulfur atom and
the noncoordinated oxygen atoms [1.419(4), 1.428(4) Å],
(20) Loh, S.-K.; Mok, K. F.; Leung, P.-H.; White, A. J . P.; Williams,
D. J . Tetrahedron: Asymmetry 1996, 45.
(21) Fornie´s, J .; Navarro, R.; Sicilia, V.; Toma´s, M. Inorg. Chim. Acta
1990, 168, 201.
whereas in [Pd{C(dO)(CH2)2NEt2}(OTf)(NEt2H)], the
three S-O bond distances are not significantly differ-
ent.19
(22) (a) Herrmann, W. A.; Brossmer, C.; Priermeier, T.; Ofele, K. J .
Organomet. Chem. 1994, 481, 97. (b) Brown, J . M.; Perez-Torrente, J .
J .; Alcock, N. W.; Clase, H. J . Organometallics 1995, 14, 207. (c)
Schmid, R.; Foricher, J .; Cereghetti, M.; Schonholzer, P. Helv. Chim.
Acta 1991, 74, 370. (d) Leitch, J .; Salem, G.; Hockless, D. C. R. J . Chem.
Soc., Dalton Trans. 1995, 649. (e) Airey, A. L.; Swiegers, G. F.; Willis,
A. C.; Wild, S. B. J . Chem. Soc., Chem. Commun. 1995, 693. (f) Dufaud,
V.; Thivolle-Cazat, J .; Basset, J . M.; Mathieu, R.; J aud, J .; Waisser-
mann, J . Organometallics 1991, 10, 4005. (g) Fornie´s, J .; Martinez,
F.; Navarro, R.; Tomas, M.; Urriolabeitia E. P. J . Chem. Soc., Dalton
Trans. 1994, 505.
(23) (a) Miki, K.; Kasai, N.; Kurosawa, H. Acta Crystallogr. 1988,
C44, 1135. (b) Arlen, C.; Pfeffer, M.; Bars, O.; Le Borgne, G. J . Chem.
Soc., Dalton Trans. 1986, 359. (c) Gabbitas, N.; Salem, G.; Sterns, M.;
Willis, A. C. J . Chem. Soc., Dalton Trans. 1993, 3271. (d) Steffey, B.
D.; Miedaner, A.; Maciejewski-Farmer, M. L.; Bernatis, P. R.; Herring,
A. M.; Allured, V. S.; Carperos, V.; DuBois, D. L. Organometallics 1994,
13, 4844. (e) Mateo, C.; Ca´rdenas, D. J .; Ferna´ndez-Rivas, C.; Echa-
varren, A. M. Chem. Eur. J . 1996, 2, 1596.
(16) (a) Villanueva, L. A.; Abboud, K.; Boncella, J . M. Organome-
tallics 1991, 10, 2969. (b) Granell, J .; Sainz, D.; Sales, J .; Solans, X.;
Font-Altaba, M. J . Chem. Soc., Dalton Trans. 1986, 1785. (c) Granell,
J .; Sales, J .; Vilarrasa, J .; Declerq, J . P.; Germain, G.; Miravitlles, C.;
Solans, X. J . Chem. Soc., Dalton Trans. 1983, 2441. (d) Butler, I. R.;
Kalaji, M.; Nehrlich, L.; Hurthouse, M.; Karaulov, A. I.; Malik, K. M.
A. J . Chem. Soc., Chem. Commun. 1995, 459. (e) Blake, A. J .; Holder,
A. J .; Roberts, Y. V.; Schro¨der, M. J . Chem. Soc., Chem. Commun. 1993,
260.
(17) Cecconi, F.; Ghilardi, C. A.; Midollini, S.; Moneti, S.; Orlandini,
A.; Scapacci, G. J . Chem. Soc., Dalton Trans. 1989, 211.
(18) Stang, P. J .; Cao, D. H.; Poulter, G. T.; Arif, A. M. Organome-
tallics 1995, 14, 1110.
(19) Anderson, O. P.; Packard, A. B. Inorg. Chem. 1979, 18, 1129.

Phosphine and Aryl Ligands in Palladium Complexes
Organometallics, Vol. 16, No. 10, 1997 2135
Ta ble 2. Selected Bon d Dista n ces (Å) a n d An gles (d eg) for Com p lexes 2c, 4b′, 5, a n d 6
2c 4b′
5
6
Pd-C(11)
Pd-P(3)
Pd-P(1)
Pd-Cl
Pd-N(2)
N(1)-N(2)
P(1)-C(1)
P(2)-C(1)
P(3)-C(2)
P(4)-C(2)
1.987(3)
2.3217(8)
2.3298(8)
2.4119(8)
2.634(2)
1.259(3)
1.830(3)
1.851(3)
1.825(3)
1.840(3)
Pd-C(11)
Pd-N(2)
Pd-O(1)
Pd-P
1.979(3)
2.121(2)
2.186(2)
2.2742(7)
1.267(3)
1.397(3)
1.416(3)
1.420(3)
1.484(2)
Pd-C(11)
Pd-O(1)
Pd-P(2)
1.975(5)
2.184(4)
2.331(2)
2.339(2)
2.576(4)
1.263(6)
1.419(4)
1.428(4)
1.453(4)
Pd-C(91)
Pd-P(2)
2.040(5)
2.3181(15)
2.3243(15)
2.3592(15)
1.842(5)
1.833(5)
1.837(5)
1.828(6)
1.250(6)
Pd-P(3)
Pd-P(1)
Pd-P(1)
N(1)-N(2)
ClO(4)
Pd-N(2)
N(1)-N(2)
S(1)-O(2)
S(1)-O(3)
S(1)-O(1)
P(1)-C(1)
P(2)-C(1)
P(3)-C(2)
P(4)-C(2)
N(1)-N(2)
Cl-O(3)
Cl-O(2)
Cl-O(1)
C(11)-Pd-P(3)
C(11)-Pd-P(1)
P(3)-Pd-Cl
87.92(8)
89.43(8)
93.04(3)
89.58(3)
71.89(10)
96.46(6)
86.45(6)
108.57(5)
C(11)-Pd-N(2)
N(2)-Pd-O(1)
C(11)-Pd-P
O(1)-Pd-P
79.06(10)
97.61(8)
93.86(8)
90.01(6)
C(11)-Pd-P(2)
O(1)-Pd-P(2)
C(11)-Pd-P(1)
O(1)-Pd-P(1)
C(11)-Pd-N(2)
O(1)-Pd-N(2)
P(2)-Pd-N(2)
P(1)-Pd-N(2)
88.2(2)
92.16(11)
90.6(2)
91.19(11)
73.7(2)
98.54(14)
93.80(11)
101.51(11)
C(91)-Pd-P(2)
C(91)-Pd-P(3)
P(2)-Pd-P(1)
P(3)-Pd-P(1)
P(2)-C(1)-P(1)
P(4)-C(2)-P(3)
96.20(14)
90.69(14)
70.38(5)
102.61(5)
94.4(2)
P(1)-Pd-Cl
C(11)-Pd-N(2)
P(3)-Pd-N(2)
P(1)-Pd-N(2)
Cl-Pd-N(2)
120.8(3)
F igu r e 4. Crystal structure of the cation of complex 6.
F igu r e 2. Crystal structure of complex 5.
F igu r e 5. Crystal structure of the cation of complex 7a .
F igu r e 3. Crystal structure of complex 4b′.
displays possible C-H‚‚‚O hydrogen bonds: C1-H1B‚‚‚
O1 (1 - x, -y, 1 - z; 3.25, 2.47 Å, 136°); C14-H14‚‚‚
O2 (x, y, 1 + z; 3.41, 2.48 Å, 163°); and C26-H26‚‚‚
O3 (1 + x, y, 1 + z; 3.31, 2.48 Å, 137°).
The crystal structures of the aquo complexes 9 and
10 (Figures 6 and 7 and Table 3) show the azophenyl
ligand acting as a chelating ligand, the phosphine ligand
bonded trans to the N(2) atom and one coordinated
molecule of water. In 10, a second water molecule is
hydrogen bonded to the aquo ligand. The resulting
cationic units are connected by the anion through
hydrogen bonds, leading to an isotactic (9) or syndio-
tactic (10) polymer (Scheme 5 and Figures 7 and 8).
Hydrogen bonding parameters for 9 are O1-H1‚‚‚O2
2.721, 1.96 Å, 159°; O1-H2‚‚‚O3 (1 - x, -0.5 + y,1.5 -
z) 2.618, 1.83 Å, 176° and for 10 are O1‚‚‚H1-O6 2.673,
1.87 Å, 174°; O1-H2‚‚‚O3 2.855, 2.11 Å, 154°; O6-
H3‚‚‚O3 (1 - x, 1 - y, 1 - z) 2.987, 2.18 Å, 177°; and

2136 Organometallics, Vol. 16, No. 10, 1997
Vicente et al.
Ta ble 3. Selected Bon d Dista n ces (Å) a n d An gles (d eg) for Com p lexes 7a , 9, 10, a n d 11
7a 10 11
9
Pd-C(11)
Pd-N(2)
Pd-P(1)
2.056(10)
2.096(8)
2.259(3)
2.413(3)
1.829(10)
1.858(10)
1.258(11)
Pd-C(11)
Pd-N(2)
Pd-O(1)
Pd-P
1.987(5)
2.115(4)
2.139(4)
2.2673(13)
1.264(5)
1.405(4)
1.405(5)
1.436(5)
Pd-C(11)
Pd-N(2)
Pd-O(1)
Pd-P
N(1)-N(2)
Cl-O(5)
Cl-O(2)
Cl-O(4)
Cl-O(3)
1.991(3)
2.093(3)
2.141(3)
2.2753(12)
1.266(4)
1.426(3)
1.433(3)
1.433(3)
1.453(3)
Pd-C(11)
Pd-N(2)
Pd-O(1)
Pd-P(1)
P1C1
P2C1
P(2)-O(1)
N(1)-N(2)
1.993(8)
2.117(7)
2.134(5)
2.261(2)
1.850(8)
1.806(9)
1.519(6)
1.267(9)
Pd-P(2)
P(1)-C(1)
P(2)-C(1)
N(1)-N(2)
N(1)-N(2)
S-O(4)
S-O(2)
S-O(3)
C(11)-Pd-N(2)
C(11)-Pd-P(1)
N(2)-Pd-P(2)
P(1)-Pd-P(2)
P(1)-C(1) P(2)
77.3(4)
C(11)-Pd-N(2)
N(2)-Pd-O(1)
C(11)-Pd-P
O(1)-Pd-P
79.5(2)
C(11)-Pd-N(2)
N(2)-Pd-O(1)
C(11)-Pd-P
O(1)-Pd-P
79.55(13)
90.26(11)
95.55(11)
94.69(8)
C(11)-Pd-N(2)
N(2)-Pd-O(1)
C(11)-Pd-P(1)
O(1)-Pd-P(1)
P(2)-C(1)-P(1)
P(2)-O(1)-Pd
79.7(3)
97.5(2)
94.8(2)
87.8(2)
107.0(4)
116.8(3)
101.1(3)
111.1(2)
70.36(9)
93.9(4)
91.89(15)
94.80(15)
94.21(11)
Sch em e 5
F igu r e 6. Crystal structure of complex 9.
F igu r e 7. Crystal structure of complex 10.
O6-H4‚‚‚O2 (1 + x, y, z) 2.898, 2.10 Å, 172°. Among
the few reported crystal structures of aquopalladium-
(II) complexes,18,24 five are reported to show interactions
(24) (a) Benetollo, F.; Bertani, R.; Bombieri, G.; Toniolo, L. Inorg.
Chim. Acta 1995, 233, 5. (b) Sheehan, J . P.; Spalding, T. R.; Ferguson,
G.; Gallagher, J . F.; Kaitner, B.; Kennedy, J . D. J . Chem. Soc., Dalton
Trans. 1993, 35. (c) Seligson, A. L.; Trogler, W. C. Organometallics
1993, 12, 738. (d) Castan, P.; J aud, J .; Wimmer, S.; Wimmer F. L. J .
Chem. Soc., Dalton Trans. 1991, 1155. (e) Deeming, A. J .; Rothwell, I.
P.; Hursthouse, M. B.; New, L. J . Chem. Soc., Dalton Trans. 1978,
1490. (f) Maassarani, F.; Pfeffer, M.; Le Borgne, G. Organometallics
1987, 6, 2043. (g) Kickham, J . E.; Loeb, S. J . Organometallics 1995,
14, 3584. (h) Vicente, J .; Arcas, A.; Borrachero, M. V.; Mol´ıns, E.;
Miravitlles, C. J . Organomet. Chem. 1992, 441, 487. (i) Leoni, P.;
Sommovigo, M.; Pasquali, M.; Midollini, S.; Braga, D.; Sabatino, P.
Organometallics 1991, 10, 1038.
F igu r e 8. Crystal structure of the cation of complex 11.
between the anion and the water molecule.18,24a,h,i Al-
though this interaction is always through hydrogen
bonds, these structures and those of 9 and 10 display
five different structural motifs, as shown in Scheme 5.
Most aquopalladium(II) complexes exhibit very simi-
lar Pd-O bond distances (range 2.106(4)-2.141(3) Å for

Phosphine and Aryl Ligands in Palladium Complexes
Organometallics, Vol. 16, No. 10, 1997 2137
those with reasonable precision)18,24a,d,f regardless of the
nature of the trans ligand (aryl or alkyl phosphine) or
the presence or absence of hydrogen bonds between the
aquo ligand and the anion. The Pd-O bond distances
in 9 (2.139(4) Å) and 10 (2.141(3) Å) are thus among
the longest. Out of this range are the metallaheterobo-
rane [2-(H2O)-2-(PPh3)-closo-2,1-PdTeB10H9(PPh3)]BF4
dppm)(η2-dppm)]Cl:[Pd(C6H3N2To-2,Me-5)Cl(η1-dppm)2]:
trans-[Pd(C6H3N2Me-2,To-5)Cl(µ-dppm)]2 are 4:2:1 at
-60 °C.
The 31P NMR spectrum of 6 at room temperature
shows broad resonances in the region from -20 to -32
ppm. At -60 °C a first-order spectrum is observed
corresponding to four different nuclei of the static
structure of complex 6.
(2.208(4) Å),24b the metalated phosphine [Pd{PBut -
2
Mu tu a lly tr a n s P h osp h in e a n d Ar yl Liga n d s.
The difficulty in preparing cis-[Pd(Ar)X(PPh3)2] com-
plexes was first observed by Pfeffer26 and was related
to the antisymbiotic effect. According to this effect, two
soft ligands in mutually trans positions will have a
destabilizing effect on each other when attached to class
b metal atoms.27 This effect has been used to explain
the geometries of metal complexes2b,3,28 and also to
discuss linkage isomerism of some ligands.29 We believe
that this effect is also responsible for all the above-
mentioned coupling reactions. In particular, the de-
composition reaction of [Pd(Ar)(Ar′)(PPh3)2] complexes
to give biaryls (Scheme 1) is a consequence of the phobia
of all pairs of ligands Ar/Ar′, Ar/PPh3, and Ar′/PPh3
against being trans. However, it seems that such a
destabilizing effect between the pair Ar/Ar′ is greater
than that for Ar/PPh3, and this is the reason for
obtaining cis-[Pd(Ar)(Ar′)(PPh3)2]. The geometry of the
resulting complex and the destabilizing effect of both
Ar/PPh3 and Ar′/PPh3 pairs of ligands in trans positions
explains the coupling of the aryl groups to give Ar-Ar′.
A search of the Cambridge Structural Database
reveals only one crystal structure of a trans-diarylpal-
ladium(II) complex, [Pd(C6F5)2{PPh2CH2Ph2PAu(C6-
F5)}2],30 and only one of a diarylpalladium(II) complex
containing a trans phosphine ligand, cis-[Pd(C6F5)2-
(PPh3)2].23a Probably, the first complex adopts a trans
geometry because of the steric hindrance of the large
phosphine ligands and the second one, which has the
expected cis geometry, does not give the corresponding
biaryl because of the two very strong C-Pd bonds. Most
reported structures of monoarylpalladium complexes do
not have a phosphine trans to the aryl group. In the
few that do, the trans coordination of phosphine and
carbon donor ligands is forced by the nature of the
phosphine,22,23c,d the complex,16a or the aryl group.23b In
addition, there are no reported crystal structures of
monoarylpalladium complexes containing the aryl and
(CH2)2CH(CH2)2PBut }(H2O)]BPh4 (2.301(6) Å),24c and
2
trans-[PdH(PCy3)2(H2O)]BF4 (2.206(5) Å),24i in which
very bulky cis ligands prevent optimal binding of the
water molecule. In complex 9, the S-O(3) distance
(1.435(5) Å) is significantly longer that the other two
S-O distances (1.405(4) and 1.405(5) Å) and the same
occurs in 10, with Cl-O(3) (1.453(3) Å) longer than the
other three (1.426(3), 1.433(3), and 1.433(3) Å). There
is no obvious explanation in terms of H-bonding interac-
tions, since the H bond acceptors in 9 are O2 and O3
and in 10 are O2 and O3 (the latter accepting two H
bonds).
The crystal structure of 11 (see Figure 8) shows that
the oxidation of dppm in complex 7b has occurred at
the phosphorus atom trans to the aryl group. As far as
we are aware, the crystal structure of 11 is the first of
a palladium complex with dppmO. The P-O (1.519(6)
Å) bond distance is normal.25
Sp ectr oscop ic P r op er ties of Com p lexes. The
NMR data of complexes 1-13 are in agreement with
the proposed structures. In the 31P NMR spectra of
complexes containing chelating dppm (6, 7), the chemi-
cal shift of the phosphorus trans to the aryl ligand (PX;
Chart 2) appears at high field (-33.32 and -30.60 ppm),
near the value of the chemical shift of the nonbonded
phosphorus in 6 (δ(PQ) ) -32.52 ppm).
Equilibria among different species in solutions of
trans-[Pd(C6H3N2To-2, Me-5)Cl(η1-dppm)2] (2c) and a
fluxional behavior in the case of [Pd(C6H3N2To-2, Me-
5)(η1-dppm)(η2-dppm)]TfO (6) are observed. Thus, at
1
room temperature, the H NMR spectrum of 2c shows
broad resonances around 4 and 3.2 ppm and several
singlets in the region 1.5-2.6 ppm corresponding,
respectively, to CH2 and Me groups of different dppm
and azotolyl ligands. At -60 °C, six singlets corre-
sponding to three different azotolyl ligands (see assign-
ment in the Experimental section) and several multip-
lets (difficult to assign) are observed. The 31P NMR
spectrum at -60 °C shows the following subspectra: a
first-order spectrum corresponding to four different
nuclei, corresponding to the complex [Pd(C6H3N2To-2,-
Me-5)(η1-dppm)(η2-dppm)]Cl (by comparison with 6); two
singlets corresponding to the dimer 3a and free dppm;
two deceptively simple triplets of an AA′XX′ system,
corresponding to the static structure of complex 2c.
These data can be explained if the following equilibria
are assumed: [Pd(C6H3N2To-2,Me-5)Cl(η1-dppm)2] h
[Pd(C6H3N2To-2,Me-5)(η1-dppm)(η2-dppm)]Cl and [Pd-
(C6H3N2To-2,Me-5)Cl(η1-dppm)2] h 1/2trans-[Pd(C6H3N2-
(26) Dehand, J .; J ordanov, J .; Pfeffer, M.; Zinsius, M. C. R. Acad.
Sci., Ser. C 1975, 281, 651. Pfeffer, M.; Grandjean, D.; Le Borgne, G.
Inorg. Chem., 1981, 20, 4426.
(27) Pearson, R. G. Inorg. Chem. 1973, 12, 712.
(28) J edlicka, B.; Ru¨lke, R. E.; Weissensteiner, W.; Ferna´ndez-Gala´n,
R.; J alo´n, F. A.; Manzano, B. R.; Rodriguez de la Fuente, J .; Veldman,
N.; Kooijman, H.; Spek, A. L. J . Organomet. Chem. 1996, 516, 97.
Casares, J . A.; Coco, S.; Espinet, P.; Lin, Y.-S. Organometallics 1995,
14, 3058. Crabtree, R. H.; Davis, M. W.; Mellea, M. F.; Mihelcic, J . M.
Inorg. Chim. Acta 1983, 72, 223. Holloway, C. E.; Stynes, D. V.; Vuik,
C. P. J . J . Chem. Soc., Dalton Trans. 1982, 95. Cooke, R. R.;
Burmeister, J . L. J . Organomet. Chem. 1973, 63, 471. Vicente, J .;
Bermudez, M. D.; Carrion, F. J .; J ones, P. G. J . Organomet. Chem.
1996, 508, 53. Vicente, J .; Abad, J . A.; Fernandez-de-Bobadilla, R.;
J ones, P. G.; Ramirez de Arellano, M. C. Organometallics 1996, 15,
24. Vicente, J .; Saura-Llamas, I.; Palin, M. G.; J ones, P. G. J . Chem.
Soc., Dalton Trans. 1995, 2535. Vicente, J .; Bermudez, M. D.; Vicente,
J .; Bermudez, M. D.; Carrillo, M. P.; J ones, P. G. J . Chem. Soc., Dalton
Trans. 1992, 1975.
1
Me-2,To-5)Cl(µ-dppm)]2 + dppm. According to the H
NMR spectrum, the ratios of [Pd(C6H3N2To-2,Me-5)(η1-
(29) Akhtar, M. N.; Isab, A. A.; Al-Arfaj, A. R.; Hussain, M. S.
Polyhedron 1997, 16, 125. Melpolder, J . B.; Burmeister, J . L. Inorg.
Chim. Acta 1981, 49, 115. Artz, R. S.; Burmeister, J . L. Inorg. Chim.
Acta 1980, 40, 31. DeStefano, N. J .; Burmeister, J . L. Inorg. Chem.
1971, 10, 998.
(30) Uso´n, R.; Laguna, A.; Fornies, J .; Valenzuela, I.; J ones, P. G.;
Sheldrick, G. M. J . Organomet. Chem. 1984, 273, 129.
(25) Rossi, R.; Marchi, A.; Marvelli, L.; Magon, L.; Peruzzini, M.;
Casellato, U.; Graziani, R. Inorg. Chim. Acta 1993, 204, 63. Wegman,
R. W.; Abatjoglou, A. G.; Harrison, A. M. J . Chem. Soc., Chem.
Commun. 1987, 1891. Fontaine, X. L. R.; Fowles, E. H.; Layzell, T. P.;
Shaw, B. L.; Thornton-Pett, M. J . Chem. Soc., Dalton Trans. 1991,
1519.

2138 Organometallics, Vol. 16, No. 10, 1997
Vicente et al.
PPh3 ligands in trans positions. However, an interest-
ing and rare familly of palladacycles containing PPh3
and other phosphines trans to an aryl ligand has
recently been reported. As the authors point out, the
stability of these complexes is due to the high energy of
the expected C-C coupling products.23e
the intermediate complex, [Pd(Ar)(NR′R′′)(PR3)2], is the
most stable trans isomer (no Ar/PPh3 in trans). It is so
stable that no coupling process occurs. The use of
potentially chelating diphosphines, such as 1,2-bis-
(diphenylphosphino)ethane (dppe), also fails to give the
desired anilines because they can easily bond as mono-
coordinate ligands (e.g., trans-[Pd(Ar)(NR′R′′)(dppe)2]
similar to 2c) or in a bridging mode (e.g., trans-[Pd(Ar)-
(NR′R′′)(µ-dppe)]2 similar to 3a ,b) that in any case
would give the desired trans Ar/PR3 coordination.
The aforementioned facts, the synthesis of complexes
6, 7a -c, and 8, and our unsuccessful attempts to
prepare [Pd(C6H3NdNR-2,X-5)(PPh3)2]+ (X ) Me, H; R
) To, Ph) (Scheme 2),3 as well as Pfeffer’s failure to
prepare similar cyclometalated complexes,23b,26 suggests
that the antisymbiotic effect is greater for PPh3 than
for P(alkyl)3. In addition, the successful synthesis of
Con clu sion s
A family of palladium 2-(arylazo)aryl complexes with
phosphines has been isolated, and the crystal structures
of eight of them have been determined. Most of these
structures correspond to complexes with weak donor
ligands (such as triflato, perchlorato, or aquo) or with
phosphines coordinated trans to the aryl ligand. For
the first group, there are very few precedents. We
report new types of aquo complexes of palladium. The
crystal structures of two complexes containing chelating
dppm show a large value of ∆ ) (Pd-Ptrans to aryl) - (Pd-
Pcis to aryl). The weakening of the Pd-Ptrans to aryl bond
is responsible for the fluxional behavior of [Pd(C6H3N2-
To-2,Me-5)(η1-dppm)(η2-dppm)]TfO (6) and the facile
[Pt(C6H3NdNTo-2,Me-5)(PPh3)2]OTf (13) means that
the destabilizing effect between the pair of ligands Ar/
PPh3 is greater for palladium than that for platinum.
Furthermore, the facile oxidation of 7b can be related
to the weak Pd-Ptrans to aryl bond. We are aware of
examples of such oxidations when the oxidized phos-
phorus atom is a noncoordinated atom of a bi- or
tridentate phosphorus ligand22g,31 but, as far as we are
aware, never when the phosphine is acting as a chelat-
ing ligand. It can be concluded that this destabilizing
effect affects both ligands in trans positions and that
not only can it induce coupling processes but also other
transformations that avoid the Ar/PPh3 trans geometry.
A different view of this destabilizing effect is that it
increases with the trans influence of the ligands. Thus,
the order of decreasing trans influence Ar > PR3
requires the following order Ar/Ar > Ar/PR3 > PR3/PR3
for the phobia of ligands to be trans to each other.
A clear example of application of these ideas is
furnished by the very recent and simultaneous reports
of Buchwald and Hartwig about a second generation of
palladium catalysts for cross-coupling of aryl halides
with amines.6 Both have found that a Pd(0)/PP catalyst,
where PP is a strongly chelating diphosphine, improves
the result, allowing it to work with primary amines or
aryl iodides and also leading to better yields in some
cases for which poor results were previously obtained.
According to the authors’ data, the product from the
oxidative addition reaction reacts with R′R′′N- to give
cis-[Pd(Ar)(NR′R′′)(PP)] (Scheme 2). In our opinion, the
coupling to give ArNR′R′′ occurs because of the desta-
bilizing effect of the aryl and phosphine ligands in the
trans positions. Such couplings do not occur when PPh3
and similar monodentate phosphines are used because
oxidation of [Pd(C6H4NdNPh-2)(η2-dppm)]SbF6 (7b). We
also report the structure of two complexes with weak
Pd‚‚‚N interactions (2c, 5), one of which posseses a
coodination plane which is markedly folded about a
L-Pd-L axis, with interesting C-H‚‚‚O contacts that
may be described as hydrogen bonds (5, 6) and the best
way to prepare 2-(arylazo)aryl platinum complexes. The
data we present in this paper, together with observa-
tions we and others have previously made, shows the
difficulty of coordinating a phosphine trans to an aryl
ligand in palladium complexes. We propose to name
this destabilizing effect as transphobia.
Ack n ow led gm en t. We thank Direccio´n General de
Investigacio´n Cient´ıfica y Te´cnica (PB92-0982-C) and
the Fonds der Chemischen Industrie for financial sup-
port. D.B. thanks Ministerio de Educacio´n y Ciencia
(Spain) for a grant.
Su p p or tin g In for m a tion Ava ila ble: Tables of all crystal
data and structure refinement details, refined and calculated
atomic coordinates, anisotropic thermal parameters, and bond
lengths and angles for compounds 2c‚1/2CH2Cl2, 4b′, 5, 6, 7a ,
9, 10, and 11‚2MeOH (61 pages). Ordering information is
given on any any current masthead page.
(31) Rashidi, M.; Vittal, J . J .; Puddephatt, R. J . J . Chem. Soc.,
Dalton Trans. 1994, 1283.
OM961094H