Structural properties and dissociative fluxional motion of 2,9-dimethyl-1,10-phenanthroline in platinum(II) complexes

Inorg. Chem. 2005, 44, 1248−1262

Structural Properties and Dissociative Fluxional Motion of

2,9-Dimethyl-1,10-Phenanthroline in Platinum(II) Complexes

Raffaello Romeo,*^,†Salvatore Carnabuci,^†Maria Rosaria Plutino,^‡Andrea Romeo,^†Silvia Rizzato,^§and

Alberto Albinati^§

Dipartimento di Chimica Inorganica, Chimica Analitica e Chimica Fisica, UniVersita` di Messina,

Salita Sperone 31, Vill. S. Agata 98166, Messina, Italy, Istituto Materiali Nanostrutturati,

ISMN - CNR, Unita` di Messina, Sezione di Palermo, Italy, and Dipartimento di Chimica

Strutturale (DCSSI) e Facolta` di Farmacia, Via Venezian 21, UniVersita` di Milano, Milano, Italy

Received October 8, 2004

A dynamic ¹H NMR study has been carried out on the fluxional motion of the symmetric chelating ligand 2,9-

dimethyl-1,10-phenanthroline (Me₂-phen) between nonequivalent exchanging sites in a variety of square-planar

complexes of the type [Pt(Me)(Me₂-phen)(PR₃)]BArf, 1

P-donor ligands PR₃encompass a wide range of steric and electronic characteristics [PR₃

1, F, 2, Cl 3, CF₃4, MeO 5, Me 6; PR₃PMe(C₆H₅)₂7, PMe₂(C₆H₅) 8, PMe₃9, PEt₃10, P(i-Pr)₃11, PCy(C₆H₅)₂

12, PCy₂(C₆H₅) 13, PCy₃14]. All complexes have been synthesized and fully characterized through elemental

analysis, ¹H and ³¹P ¹H

NMR. X-ray crystal structures are reported for the compounds 8, 11, 14, and for [Pt-

(Me)(phen)(P(C₆H₅)₃)]PF₆(15), all but the last showing loss of planarity and a significant rotation of the Me₂-phen

moiety around the N1 N2 vector. Steric congestion brought about by the P-donor ligands is responsible for tetrahedral

distortion of the coordination plane and significant lengthening of the Pt N₂(cis to phosphane) bond distances.

−14, (BArf

)

B[3,5-(CF₃)₂C₆H₃]₄). In these compounds, the

)

P(4-XC₆H₄)₃, X

) H

)

{

}

−

Application of standard quantitative analysis of ligand effects (QALE) methodology enabled a quantitative separation

1

of steric and electronic contributions of P-donor ligands to the values of the platinum

−

phosphorus J_PtPcoupling

−

°

constants and of the free activation energies

∆

G^qof the fluxional motion of Me₂-phen in 1

and 148°

14. The steric profiles

1

for both J_PtPand

∆

G^qshow the onset of steric thresholds (at cone angle values of 150

, respectively),

that are associated with an overload of steric congestion already evidenced by the crystal structures of 11 and 14.

The sharp increase of the fluxional rate of Me₂-phen can be assumed as a perceptive kinetic tool for revealing

ground-state destabilization produced by the P-donor ligands. The mechanism involves initial breaking of a metal

nitrogen bond, fast interconversion between two 14-electron three-coordinate T-shaped intermediates containing

¹-coordinated Me₂-phen, and final ring closure. By use of the results from QALE regression analysis, a free-

energy surface has been constructed that represents the way in which any single P-donor ligand can affect the

−

η

energy of the transition state in the absence of aryl or

π-acidity effects.

Introduction

steric in nature. Steric hindrance brought by the methyl

substituents of Me₂-phen in proximity to other groups

coordinated to the metal favors a pronounced distortion of

the ligand that is observed in a number of X-ray studies of

similar compounds.³This distortion may be measured by the

dihedral angle between the plane of the chelating moiety and

that of the square-planar coordination plane. For instance,

the complex [Pt(Me)(Me₂-phen)(Me₂SO)]⁺exhibits a flux-

The bidentate nitrogen ligand 2,9-dimethyl-1,10-phenan-

throline (Me₂-phen), when coordinated to monoalkyl cationic

platinum(II) complexes of the type [Pt(Me)(Me₂-phen)(L)]⁺,

exhibits a fast fluxional motion between two nonequivalent

exchanging sites.^1,2The origin of the phenomenon is mainly

* Author to whom correspondence should be addressed. E-mail:

Raf.Romeo@chem.unime.it. Fax: ++39-090-393756. Phone: ++39-090-

6765717.

(1) Romeo, R.; Fenech, L.; Monsu` Scolaro, L.; Albinati, A.; Macchioni,

A.; Zuccaccia, C. Inorg. Chem. 2001, 40, 3293-3302.

(2) Romeo, R.; Fenech, L.; Carnabuci, S.; Plutino, M. R.; Romeo, A. Inorg.

Chem. 2002, 41, 2839-2847.

^†Universita` di Messina.

^‡Istituto Materiali Nanostrutturati.

^§Universita` di Milano.

1248 Inorganic Chemistry, Vol. 44, No. 5, 2005

10.1021/ic0485920 CCC: $30.25

Published on Web 02/10/2005

2,9-Dimethyl-1,10-Phenanthroline in Platinum(II) Complexes

ional behavior while [Pt(Me)(phen)(Me₂SO)]⁺, with the

phenanthroline plane lying almost coplanar with the coor-

dination plane,⁴features a static structure. In the substrate

containing Me₂-phen, the same specific nonbonding repul-

sions by the 2,9 methyl groups that promote the chelate

flipping must be held responsible for the high lability of Me₂-

SO. The ligand exchange with uncoordinated Me₂SO takes

place at a rate (k₂) 38 × 10³m^-1s^-1) that is 5 orders of

magnitude higher than that of the complex containing

unsubstituted phen (k₂) 0.18 m^-1s^-1) or even of complexes

with alkyl or aryl substituents at the periphery of phenan-

throline (3,4,7,8-Me₄phen, k₂) 0.026 m^-1s^-1; 4,7-Ph₂phen,

k₂) 0.10 m^-1s^-1).⁵This represents a rare, if not a unique,

case of steric acceleration in associative nucleophilic sub-

stitutions at square-planar complexes, accounted for by the

propensity of the dinitrogen ligand to form a flat uncon-

strained five-membered ring in the trigonal plane of the five-

coordinate intermediate. Steric relief is also at the origin of

the easy direct uptake of strong π-acceptor ligands, such as

alkene or alkyne by [PtX₂(Me₂-phen)] (X ) halide ions)

complexes to form discrete and stable five-coordinate trigonal

bipyramidal species.^6-8

on the interionic structure of the complex and the action of

potential nucleophiles. The first process is prevalent within

the ion pairs, detected by ¹⁹F{¹H} HOESY NMR spectra

-

and formed by “noncoordinating” anions (X ) PF₆, BF₄,

etc.) with the cationic complex in nonpolar solvents.¹Among

the possible associative mechanisms promoted by polar

solvents or by relatively strong nucleophiles such as sulfides

or sulfoxides, a consecutive stepwise displacement mecha-

nism is preferred to intramolecular rearrangements (Berry

pseudorotation or turnstile) of five-coordinated intermedi-

ates.²Both dissociative and associative mechanisms involve

ring opening and Pt-N bond rupture.

Compounds similar to 1, where PPh₃has been substituted

by less efficient trans-activating groups L (amine, pyridine,

or thiourea), behave as stereochemically rigid N-N chelate

complexes.¹This indicates that electronic factors also come

into play and are connected to the capacity of the ligand L

of promoting Pt-N bond dissociation. Within this mecha-

nistic framework, we thought it could be worthwhile to

extend our previous study to the fluxionality of [Pt(Me)-

(Me₂-phen)(L)]⁺complexes, including P-donor ligands with

widely different electronic and steric properties. Moreover,

the application of QALE methodology enabled the rate

constants and the NMR data to be analyzed according to

the electronic and steric characteristics of the ligands.

On substituting Me₂SO with a firmly bonded ligand, as

in [Pt(Me)(Me₂-phen)(PPh₃)]⁺(1), ligand exchange is blocked

and the only possible dynamic motion remains the flipping

of Me₂-phen that was previously investigated by variable-

temperature NMR spectroscopy in CDCl₃as a function of

the counteranion, the solvent, or of added nucleophiles.^1,2

The high trans effect and trans influence of the methyl and

phosphane groups, together with the remarkable steric

congestion at the coordination plane, favor either a facile

dissociation of a Pt-N bond or the addition of a fifth group.

Thus, the mechanism is switchable between intramolecular

dissociative and bimolecular associative pathways, depending

Results

Synthesis and General Properties. The complex [Pt(Me)-

(Me₂-phen)(Me₂SO)]PF₆, prepared following a published

procedure,⁵was used as a useful synthon for the formation

of the corresponding salts containing a wide series of P-donor

ligands, taking advantage of the easy removal of Me₂SO by

phosphanes, according to the substitution reaction

[Pt(Me)(Me₂-phen)(Me₂SO)]PF₆+ PR₃f

[Pt(Me)(Me₂-phen)(PR₃)]PF₆+ Me₂SO (1)

(3) (a) Klein, A.; McInnes, E. J. L.; Kaim, W. J. Chem. Soc., Dalton

Trans. 2002, 2371-2378. (b) Clark, R. J. H.; Fanizzi, F. P.; Natile,

G.; Pacifico, C.; van Rooyen, C. G.; Tocher, D. A. Inorg. Chim. Acta

1995, 235, 205-213. (c) Fanizzi, F. P.; Intini, F. P.; Maresca, L.;

Natile, G.; Lanfranchi, M.; Tiripicchio, A. J. Chem. Soc., Dalton Trans.

1991, 1007-1015. (d) Fanizzi, F. P.; Natile, G.; Lanfranchi, M.;

Tiripicchio, A.; Laschi, F.; Zanello, P. Inorg. Chem. 1996, 35, 3173-

3182. (e) De Felice, V.; Albano, V. G.; Castellari, C.; Cucciolito, M.

E.; De Renzi, A. J. Organomet. Chem. 1991, 403, 269-277. (f) Milani,

B.; Alessio, E.; Mestroni, G.; Sommazzi, A.; Garbassi, F.; Zangrando,

E.; Bresciani-Pahor, N.; Randaccio, L. J. Chem. Soc., Dalton Trans.

1994, 1903-1911. (g) Cucciolito, M. E.; De Renzi, A.; Giordano, F.;

Ruffo, F. Organometallics 1995, 14, 5410-5414.

The hexafluorophosphate salts thus obtained were con-

verted into the final [Pt(Me)(Me₂-phen)(PR₃)]BArf (BArf )

B[3,5-(CF₃)₂C₆H₃]₄) compounds 1-14 by treatment with Na-

(BArf) and separation of NaPF₆. The anion exchange of BArf

for PF₆was dictated by the well-known noncoordinating

properties of BArf and the necessity of avoiding any possible

interaction of the anion with the metal-cationic complex in

solution. Actually, the ¹⁹F{¹H} HOESY spectrum of [Pt(Me)-

(Me₂-phen)(PPh₃)] BArf 1, recorded at 260 K in CDCl₃,

showed the absence of interionic contacts between the

fluorine atoms of CF₃groups of BArf and hydrogen atoms

of the cation, indicating that the compound in chloroform is

not appreciably present as an intimate ion pair.¹

X-ray Structural Studies. ORTEP views of the cations

8, 11, 14, and 15 are shown in Figure 1, Figure 2, Figure 3,

and Figure 4, respectively. A list of relevant bond distances

and angles is given in Table 1. Compound 15, in which an

unsubstituted phenanthroline moiety (phen) is bound to the

Pt atom, may be used, by comparison to the other com-

pounds, to show the effect of the methyl substitution in

position 2,9 on the geometry of the complexes. It is worth

(4) Bruno, G.; Nicolo`, F.; Scopelliti, R.; Arena, G. Acta Crystallogr., Sect.

C 1996, 52, 827-829.

(5) Romeo, R.; Monsu` Scolaro, L.; Nastasi, N.; Arena, G. Inorg. Chem.

1996, 35, 5087-5096.

(6) (a) Albano, V. G.; Natile, G.; Panunzi, A. Coord. Chem. ReV. 1994,

133, 67-114. (b) Maresca, L.; Natile, G. Comments Inorg. Chem.

1993, 14, 349-366.

(7) (a) Albano, V. G.; Ferrara, M. L.; Monari, M.; Panunzi, A.; Ruffo, F.

Inorg. Chim. Acta 1999, 285, 70-75. (b) De Felice, V.; Ferrara, M.

L.; Giordano, F.; Ruffo, F. Gazz. Chim. Ital. 1994, 124, 117-119. (c)

Giordano, F.; Ruffo, F.; Saporito, A.; Panunzi, A. Inorg. Chim. Acta

1997, 264, 231-237. (d) Fanizzi, F. P.; Natile, G.; Lanfranchi, M.;

Tiripicchio, A.; Pacchioni, G. Inorg. Chim. Acta 1998, 275, 500-

509. (e) Albano, V. G.; Castellari, C.; Monari, M.; De Felice, V.;

Panunzi, A.; Ruffo, F. Organometallics 1996, 15, 4012-4019. (f)

Albano, V. G.; Castellari, C.; Monari, M.; De Felice, V.; Panunzi,

A.; Ruffo, F. Organometallics 1992, 11, 3665-3669.

(8) Fanizzi, F. P.; Margiotta, N.; Lanfranchi, M.; Tiripicchio, A.; Pacchioni,

G.; Natile, G. Eur. J. Inorg. Chem. 2004, 8, 1705-1713.

Inorganic Chemistry, Vol. 44, No. 5, 2005 1249

Romeo et al.

(Figure 4) shows planar phen moieties arranged to form a

“supra-unit” held together by attractive π-π stacking

interactions (inter-ring shortest distances in the range 3.5-

3.7 Å), with no Pt‚‚‚Pt interactions (d_Pt-Ptg 8.5 Å). There

are no relevant distortions from the square-planar coordina-

tion as shown by the deviation from the coordination plane

(defined by the atoms Pt, P, N1, N2, C1L) of ca. (0.04 Å.

An important feature of the Me₂-phen cations 1, 8, 11,

and 14 is that the differences in the Pt-PR₃distances (2.23-

2.25 Å) are hardly significant, irrespective of the different

basicity and steric hindrance of the P-donor ligands. These

findings are in line with the results of a recent QALE analysis

of the Rh-P bond lengths for [Rh(CO)(Cl)(PX₃)₂] com-

plexes, where it was found that π effects are dominant (53%)

over σ electronic and steric factors.⁹Likewise, the Fe-P

bond lengths of [Fe(CO)(η-Cp)(COMe)(PX₃)] vary over a

narrow range (2.195 ( 0.015 Å) and are only slightly

dependent on the σ donicity and size of the ligand.¹⁰Similar

to the Pt-P separations, the N1-Pt-N2 angles also do not

change much along the series of determined structures (cf.

Table 1).

Figure 1. ORTEP view of the cation 8 showing 50% probability ellipsoids.

The introduction of the two methyl substituents, in position

2,9 of the phenanthroline, brings substantial changes to the

coordination geometry. The most relevant is a tilt of the

dmphen moiety away from the coordination plane, as shown

by the values of the dihedral angles between the plane

defined by atoms Pt, N1, N2 and that defined by the atoms

of the phenanthroline (cf. Table 1) in the range 30-38°. A

further effect is the loss of planarity of the ligand as can be

seen by the increase of the dihedral angles between the

pyridyl moieties (in the range 4-12°). Finally, the coordina-

tion plane at the platinum(II) center undergoes a tetrahedral

distortion that can be seen from the deviations of atoms P

and C1L from the lsq planes defined by the atoms Pt1, N1,

N2 and listed in Table 1. All three effects follow the order

PCy₃> PPh₃> PPhMe₂> P(i-Pr)₃that does not reflect a

clean steric or electronic character. The same sequence is

observed in the decrease of the Pt-N1 separation (i.e., that

trans to P atom) (from 2.160(8) to 2.064(7) Å). Surprisingly,

the Pt-N1 separation for the P(i-Pr)₃-containing compound

is even shorter than that found in compound 15 containing

the unsubstituted phenanthroline (2.101(6) Å).

Figure 2. ORTEP view of the cation 11 showing 50% probability

ellipsoids.

In contrast, the Pt-N2 separations (i.e., those cis to the

PR₃ligand) show large differences (from 2.149(3) Å in [8,

R ) PhMe₂] to 2.205(7) Å in [14, R ) PCy₃]), depending

upon the steric requirements of the cis P-donor ligands. These

Pt-N bonds are long, compared with the bonds of 2.02 Å

in [Pt(bpy)₂]²⁺and [Pt(phen)₂]²⁺,¹¹showing clearly a strong

trans influence of the carbon ligand. Indeed, (cf. Figure 5)

the Pt-N2 bond length shows an exponential increase as a

Figure 3. ORTEP view of the cation 14 showing 50% probability

ellipsoids.

noticing that, in compound 15, there are three independent

molecules in the asymmetric unit. There are no significant

differences in the coordination geometries, with the exception

of the relative orientation of the phenyl rings of the

phosphane (cf. the Pt-P1-C111-C112 torsion angles in

Table 1) possibly because of the packing constraints. The

relative arrangement of the three independent molecules

(9) Wilson, M. R.; Prock, A.; Giering, W. P. Organometallics 2002, 21,

2758-2763.

(10) Liu, H.-Y.; Eriks, K.; Prock, A.; Giering, W. P. Organometallics 1990,

9, 1758-1756.

(11) (a) Dong, V.; Endres, H.; Keller, H. J.; Moroni, W.; No¨the, D. Acta

Crystallogr., Sect. B 1977, 33, 2428-2431. (b) Endres, H.; Keller, H.

J.; Moroni, W.; No¨the, D.; Dong, V. Acta Crystallogr., Sect. B 1978,

34, 1823-1827. (c) Hazell, A.; Mukhopadhyay, A. Acta Crystallogr.,

Sect. B 1980, 36, 1647-1649.

1250 Inorganic Chemistry, Vol. 44, No. 5, 2005

2,9-Dimethyl-1,10-Phenanthroline in Platinum(II) Complexes

Figure 4. ORTEP view of the cation 15 showing 50% probability ellipsoids.

function of the cone angle of the PR₃ligand. A similar

dependence is obtained by using, instead of the cone angle,

an internal steric parameter such as the symmetric deforma-

tion coordinate (S₄′′) proposed by Orpen et al,¹²(cf. Sup-

porting Information Figure S1). Values of the deformation

coordinate for the platinum(II) complexes are reported in

Table 1 and are defined by the expression

steric hindrance of the phosphane ligand. In addition, to

relieve the steric strain, the Pt-N distance cis to the

phosphane is stretched and the bond labilized. That is, the

steric bulkiness of the PR₃moiety is accommodated by (a)

the lengthening of the Pt-N2 bond and (b) the out-of-

coordination plane movement of the P atom (and if necessary

of C1L), corresponding to an overall tetrahedral distortion

from the square-planar coordination. The largest distortion

and the longest Pt-N2 and Pt-P separations are found for

the PCy₃-containing compound 14.

S₄′′ ) R₁+ R₂+ R₃- â₁- â₂- â₃

where R₁, R₂, R₃, and â₁, â₂, â₃are the C-P-C and P-C-C

angles at the coordinate phosphane, respectively. As the steric

bulk increases at the coordinate phosphane, S₄′′ decreases.

It would seem that the magnitude of phenanthroline

distortion, besides the role of the two methyl substituents in

position 2,9, is the result of a combined effect of steric and

electronic factors induced by opposite P-donor ligands. In

particular, an interesting question is to what extent this

distortion affects or is affected by the two empty molecular

orbitals very close in energy and available to accommodate

the extra electrons coming from the electron-rich metal.¹³

In contrast, it may be assumed that the observed large

deviations from the square-planar geometry are due to the

NMR Characterization and Dynamic Behavior of

Complexes 1-14. All the proton resonances of compounds

1-15 were assigned through NMR spectroscopy from the

connectivities in the 2D-NOESY experiments carried out in

chloroform-d at low temperature. The numbering scheme

1

adopted is shown in Chart 1. Selected H NMR data are

collected in Table 2, together with the ³¹P{¹H } NMR data.

1

At 250 K, the H NMR spectrum of compound [PtMe-

(Me₂-phen)(PMe₃)]BArf 9 in Figure 6, besides the reso-

nances of the aryl groups belonging to the BArf anion (δ )

7.70 and 7.47 ppm) of a methyl group directly coordinated

2

to the metal (δ 0.92, J_PtH) 72.9 Hz), and of the methyl

groups of the PMe₃ligands (δ 1.46, ³J_PtH) 45.2 Hz, ²J_PH

)

(12) Dunne, B. J.; Morris, R. B.; Orpen, A. G. J. Chem. Soc., Dalton Trans.

1991, 653-661.

(13) Klein, A.; Kaim, W.; Waldho¨r, E.; Hausen, H. D. J. Chem. Soc., Perkin

Trans. 2 1995, 2121-2126.

10.5 Hz), shows two singlets, one for each methyl (at δ )

2.97 and 2.91, respectively), four doublets for H₄(δ 8.31),

H₇(δ 8.25), H₃(δ 7.64), and H₈(δ 7.57) protons, and an

Inorganic Chemistry, Vol. 44, No. 5, 2005 1251

Romeo et al.

Table 1. Selected Bond Distances (Å) and Angles (deg) for

Compounds 1, 8, 11, 14, 15

sentially similar to those of compound 9 except for the

resonance of the methyl proton Me_Bthat is consistently

shifted to lower frequencies (at δ 1.95) as a result of ring

current from phenyl substituents on the arylphosphane bound

in the cis position. As can be seen from the data in Table 2,

a wider difference of chemical shift between the Me_Aand

Me_Bgroups of protons characterizes the ¹H NMR spectra of

the complexes containing arylphosphanes (1-6) or mixed

alkyl-arylphosphanes (7, 8, 12, 13) with respect to those of

compounds with alkylphosphanes (9-11, 14).

The passage from slow to fast exchange was followed

either through the ¹H NMR spectral changes of the aromatic

proton pair H₄-H₇or from those of the Me₂-phen methyl

groups. The process is clearly intramolecular. A lack of

exchange has been shown previously¹by a deliberate addition

of Me₂-phen to a solution of 1 in CDCl₃. In addition, for all

the examined systems 1-14 and at any temperature, there

was no indication of the presence of free phenanthroline in

solution. Unfortunately, the coupling constants of the protons

of Me₂-phen with ¹⁹⁵Pt were too weak to be observed.

However, the coupling constants of the coordinated methyl

protons and of the phosphorus atom (see Table 2) are

retained, showing values typical of methyl and phosphane

groups in the position trans to nitrogen atoms. The rate

constants for the flipping of complexes 1-14 at different

temperatures were determined by a full line-shape analysis

(Supporting Information Table S1).

PPh₃

1

PPhMe₂P(i-Pr)₃PCy₃

11 14

PPh₃

8

15^a

Bond Distances

Pt-P1

Pt-N1

Pt-N2

Pt-C11

2.233(8) 2.225(3) 2.232(2) 2.247(2) 2.224(3)

2.152(3) 2.131(2) 2.064(7) 2.160(8) 2.101(6)

2.162(3) 2.149(3) 2.184(7) 2.205(7) 2.14(1)

2.052(4) 2.124(3) 2.03(2) 2.01(1) 2.041(6)

Angles

C11-Pt-N1

C11-Pt-N2

N1-Pt-N2

C11-Pt-P1

N1-Pt-P1

N2-Pt-P1

Pt-P1-C111-C112

95.5(1)

94.4(1)

87.6(8) 93.7(4) 92.4(8)

171.4(1) 171.2(1) 163.5(8) 169.6(4) 170.8(9)

76.4(1)

86.2(1)

165.13(7) 170.74(7) 171.3(2) 159.5(2) 177(2)

100.92(7) 103.64(8) 108.6(2) 102.6(2) 99.8(6)

134.1(3) 132.6(3) 166.6(9) 166.6(6) 111.3(4),

77.5(1)

78.0(3) 76.0(3) 78.7(2)

83.94(9) 85.1(8) 87.6(3) 89.1(6)

126.1(3),

145.2(3)

Angles between lsq Planes

C10′-C6′-C6-C5-C4′-C10 ∧ 9.6(2)

8.95(2)

9.01(2)

33.8(1)

4(1)

8(1)

11.2(4) 0.7(8)

12.2(4) 1.0(8)

N1-C2-C3-C4 -C4′

C10′-C6′-C6-C5-C4′-C10 ∧ 8.7(2)

N2-C9-C8-C7-C6′-C10′

dmphen^b∧ N1-Pt-N2

36.2(1)

0.57,

0.10

29.7(3) 38.6(2) 4.01(9)

0.22,

0.29

∆d(P1), ∆d(C1l)^c

-0.35,

0.79,

-0.06 0.09

25.4 24.2

-0.08,

-0.12

deformation coordinate (S₄′′)^d

29.5

33.5

27.8

^aAverage values; for the torsion angles the values for the three

independent molecules in the asymmetric unit are listed. ESDs on the

average are obtained from the formula: σ²) ∑(x_i- xj)/(N - 1) where N

) number of observations. ^bdmphen refers to the lsq plane defined by the

atoms of the phenanthroline moiety, except the two carbons in positions

2,9. ^c∆d(P1), ∆d(C1l) are the deviations (Å) of atoms P1 and C1l, from

the lsq plane defined by the atoms Pt, N1, N2, respectively (ESDs e 0.02

Å). ^dFor the definition see text.

The activation parameters for the fluxional process were

derived from Eyring plots and are listed in Supporting

Information Table S2. In Table 3 are reported the values of

the rates (at 340 K) and of the activation energies for the

flipping of Me₂-phen, together with the values of the

stereoelectronic parameters of the P-donor ligands. Overlap-

ping of the monitored peaks with other ligand peaks for the

PCy₂(C₆H₅)-containing compound 13 prevented a satisfactory

line-shape analysis of the temperature dependence of the

NMR spectra that resulted in a poor correspondence between

experimental and simulated spectra.

Figure 5. Increase of the Pt-N2 bond separation with increasing cone

angle of the coordinated phosphanes.

Discussion

Chart 1. Structural Formula of Complexes with Atomic Numbering

The nature of the P-donor ligands L markedly affects the

rates of fluxional motion of Me₂-phen as well as the values

1

of the J_PtPcoupling constants of the [Pt(Me)(PR₃)(Me₂-

phen)]TFBP complexes (cf. data in Table 3). The efficiency

of the spectator P-donor ligands in accelerating the rear-

rangement increases in the order P(4-MeC₆H₄)₃< P(4-

MeOC₆H₄)₃< PCy(C₆H₅)₂< P(C₆H₅)₃< P(4-FC₆H₄)₃<

PMe(C₆H₅)₂< P(4-ClC₆H₄)₃< PMe₂(C₆H₅) < P(4-CF₃C₆H₄)₃

< PEt₃< PMe₃< P(i-Pr)₃< PCy₃, the difference in

reactivity between the first and the last members of the series

being 2 orders of magnitude. The entropy changes ∆S^qrange

in magnitude from -80 to +35 J K^-1mol^-1(see data in

Supporting Information Table S2), but these values must be

considered with some caution and cannot provide any real

insight into the nature of the fluxional process because of

their extreme sensitivity to systematic errors associated with

AB system for H₅(δ 7.75) and H₆(δ 7.72) protons as a

result of the asymmetry of a firmly bonded bidentate

phenanthroline.

At a higher temperature (319 K), the two methyl groups

and the aromatic proton pairs H₃-H₈, H₄-H₇, and H₅-H₆

become chemically equivalent, indicating a fast site exchange

of proton sites, which is required by interchange of the two

nitrogen atoms of the Me₂-phen ligand. The main features

1

of the H NMR phenanthroline peaks for the complex [Pt-

(Me)(Me₂-phen)(P(4-ClC₆H₄)₃]]BArf, 3 (Figure 7) are es-

1252 Inorganic Chemistry, Vol. 44, No. 5, 2005

2,9-Dimethyl-1,10-Phenanthroline in Platinum(II) Complexes

1

Table 2. Selected H and ³¹P{¹H} NMR Data for the Platinum(II) Complexes [Pt(Me)(Me₂-phen)(P)]BArf 1-15^a

δ¹H

δ³¹P

phosphane (P)

H₄

H₇

Me_A

Me_B

CH₃-Pt

others

1

2

3

4

5

6

7

8

P(C₆H₅)₃

8.32

8.33

8.27

8.32

8.33

8.30

8.31

8.25

8.23

8.29

8.33

8.29

8.88

8.15

8.21

8.26

8.18

8.15

8.10

8.13

8.25

8.18

8.22

8.18

8.22

8.25

8.68

3.02

2.99

3.00

2.97

3.02

2.97

2.95

2.94

2.98

3.03

3.00

1.90

1.92

1.95

1.86

2.02

1.95

1.97

2.13

2.91

2.92

2.01

1.85

2.93

0.74 (66.9)

0.69 (74.0)

0.69 (74.4)

0.73 (70.0)

0.75 (75.2)

0.73 (74.5)

0.90 (72.5)

1.00 (74.2)

0.92 (72.9)

0.84 (72.5)

0.96 (73.8)

0.95 (70.3)

1.03 (72.9)

0.93 (74.6)

0.92 (69.8)

7.52 (H_o,o′-P)

7.51 (H_o,o′-P)

7.40 (H_o,o′-P)

7.69 (H_o,o′-P)

14.3 (4575)

12.3 (4618)

13.2 (4622)

15.1 (4656)

9.8 (4561)

12.0 (4557)

-1.0 (4534)

-18.1 (4379)

-31.8 (4291)

3.4 (4327)

23.9 (4358)

13.7 (4501)

11.8 (4287)

13.0 (4315)

19.1 (4395)

P(4-FC₆H₄)₃

P(4-ClC₆H₄)₃

P(4-CF₃C₆H₄)₃

P(4-MeOC₆H₄)₃

P(4-MeC₆H₄)₃

PMe(C₆H₅)₂

PMe₂(C₆H₅)

PMe₃

PEt₃

P(i-Pr)₃

PCy(C₆H₅)₂

PCy₂(C₆H₅)

PCy₃

7.46 (H_o,o′-P); 3.81 (O-CH₃)

7.41 (H_o,o′-P); 2.37 (P-CH₃)

1.94 (³J_PtH) 52.7, P-CH₃)

1.76 (³J_PtH) 47.4, P-CH₃)

9

1.46 (³J_PtH) 45.2, P-CH₃)

10

11

12

13

14

15

1.72 (P-CH₂CH₃), 0.87 (P-CH₂CH₃)

2.32 (P-CHCH₃), 1.04 (P-CHCH₃)

2.62, (P-CH); 1.91, 1.62 1.25, 0.88 (C-CH₂)

2.48 (P-CH); 1.98-1.54, 1.47-1.05 (C-CH₂)

2.09 (P-CH); 1.68, 1.42, 1.14 (C-CH₂)

9.33 (³J_PtH) 35.2, H₂), 7.80 (H_o,o′-P), 7.69 (³J_PtH) 17.0, H₉)

b

P(C₆H₅)₃

2

^aRecorded in CDCl₃as solvent at appropriate temperature (see Experimental Section). Chemical shifts (δ) are in ppm and coupling constants, J_PtHfor

1

¹H and J_PtPfor ³¹P given in parentheses, are in hertz. ^bCompound containing unsubstituted 1,10-phenanthroline.

Figure 6. Section of the ¹H NMR spectrum of complex 9 recorded at

300.13 MHz in chloroform-d at 250 K (lower plot) and at 319 K (upper

plot).

Figure 7. Section of the ¹H NMR spectrum of complex 3 recorded at

300.13 MHz in chloroform-d at 260 K (lower plot) and at 354 K (upper

plot).

the line-shape analysis. The activation energies ∆G^q(340

K) are more meaningful.¹⁴

Quantitative Separation of Electronic and Steric Ef-

measures the steric requirements as derived from space-filling

fects. To correlate electronic or steric effects of the P-donor

CPK molecular models of the ligands.¹⁹Variants of the cone

ligands with any physicochemical property of the system, it

angle concept have been suggested on the basis of math-

is necessary to dissect the overall effect into its steric and

electronic components. A general and quantitative approach

(15) A complete list of references can be found in the recent papers (a)

Woska, D.; Prock, A.; Giering, W. P. Organometallics 2000, 19,

4629-4638. (b) Fernandez, A.; Reyes, C.; Lee, T. Y.; Prock, A.;

Giering, W. P.; Haar, C. M.; Nolan, S. P. J. Chem. Soc., Perkin Trans.

to the problem (QALE ) has been developed over the last

20 years, particularly by groups of Giering and Prock and

Poe¨¹⁵and has been applied to a large body of kinetic,

2000, 2, 1349-1357. (c) Fernandez, A. L.; Reyes, C.; Prock, A.;

Giering, W. P. J. Chem. Soc., Perkin Trans. 2000, 2, 1033-1041. (d)

thermodynamic, NMR, spectroscopic, and structural data.¹⁶

Babij, C.; Che, H.; Chen, L.; Poe¨, A. J. J. Chem. Soc., Dalton Trans.

Appropriate parameters for P-donor ligands are Bartik’s

infrared parameter ø, which describes the σ-electron donor

capacity of the ligands (a small ø value is associated with a

good σ donation),^17,18and Tolman’s cone angle θ, which

2003, 3184-3191. (e) Bunten, K. A.; Chen, L.; Fernandez, A. L.;

Poe¨, A. J. J. Coord. Chem. ReV. 2002, 233-234, 41-51. (f) Poe¨, A.

J.; Moreno, C. Organometallics 1999, 18, 5518-5530.

(16) http://www.bu.edu/qale. This Web site collects sets of data, protocol

for the analysis, program package, parameters of ligands, leading

references, etc. Each set of data, taken from the literature, is subjected

to a QALE analysis with commentary on how each analysis is done

and how successful it is. All the material is updated with recent data

sets and analyses.

(14) Sandstro¨m, J. Dynamic NMR Spectroscopy; Academic Press: London,

1982; ISBN 0-12-618620.

Inorganic Chemistry, Vol. 44, No. 5, 2005 1253

Romeo et al.

Table 3. Selected Kinetic and NMR Data for [Pt(Me)(Me₂-phen)(P)]BArf 1-14 Complexes and Stereoelectronic Parameters of the Corresponding

P-Donor Ligands

a

b

c

d

qe

qf

ø^a

θ^a

deg

E_ar

¹J_PtP(exp)

¹J_PtP(calc)

k_f(340)

∆G_(exp)

∆G_(calc)

phosphane

cm^-1

Hz

s^-1

kJ mol^-1

e

1

2

3

4

5

6

7

8

P(C₆H₅)₃

13.25

15.7

16.8

20.5

10.5

11.5

12.6

10.5

8.55

6.3

145

136

122

118

132

160

153

162

170

2.7

2.2

1

0

1.6

0

4575

4618

4622

4656

4561

4557

4534

4379

4291

4327

4358

4501

4287

4315

4585

4610

4621

4659

4556

4567

4517

4381

4294

4326

4353

4503

4452^g

4316

119

176

258

348

93.7

86.5

211

292

493

70.1

69.0

67.9

66.9

70.8

71.0

68.5

67.6

66.1

66.8

62.1

70.4

69.8

68.8

68.3

66.7

71.0

70.6

69.1

67.4

66.0

66.8

62.1

68.0^g

P(4-FC₆H₄)₃

P(4-ClC₆H₄)₃

P(4-CF₃C₆H₄)₃

P(4-MeOC₆H₄)₃

P(4-MeC₆H₄)₃

PMe(C₆H₅)₂

PMe₂(C₆H₅)

PMe₃

9

10

11

12

13

14

PEt₃

P(i-Pr)₃

385

2018

108

3.45

9.1

5.7

PCy(C₆H₅)₂

PCy₂(C₆H₅)

PCy₃

1.4

8029

58.2

58.1

1

^aFrom http://www.bu.edu/quale/. ^bValues of experimental J_PtPcoupling constants for complexes 1-14. ^cValues of J_PtPcoupling constants calculated

from QALE analysis. ^dRates of the fluxional motion of Me₂-phen in the complexes 1-14 at 340 K. ^eActivation energies for the flipping at 340 K. ^fActivation

energies derived from QALE analysis. ^gDeviant data treated as outliers in the QALE analysis.

ematical models,²⁰X-ray structural data,²¹or upon molecular

mechanics calculations.²²However, their use does not

necessarily improve the data analysis.^15eThe concepts of

sharp steric thresholds θ_st(below which no steric effects are

evident)²³and the so-called aryl effect E_ar(which depends

on the number of aryl groups)²⁴were introduced, as well as,

more recently, π-acidity (π_p) effects^15a,band an extension of

an apparent aryl effect to ligands that do not actually contain

aryl groups attached to the P-donor atoms.^15cIn addition,

the stereolectronic parameters for P-donor ligands (ø, θ, E_ar)

are transferable to other groups of ligands, including silyl,²⁵

arsines, nitriles,²⁶amines, thioethers,²⁷and sulfoxides.²

Equation 2 is a general form of the QALE equation for

ligands having no π-acidity (π_p) effects and systems that

might contain up to one observable steric threshold:

property ) ω + R(ø) + â(θ) + â′(θ - θ_st)λ + γ(E_ar) (2)

where ø, θ, θ_st, and E_arhave the meaning illustrated above,

λ is a switching function that equals 0 when θ < θ_stand

equals 1 when θ > θ_st. R, â, â′, and γ are regression

coefficients that measure the relative importance of elec-

tronic, steric, and aryl factors in the process. The response

of the property to ø is assumed to be linear over the entire

range of ligands, while the response to the steric parameter

(θ - θ_st) is not linear. Equation 2 allows for nonzero steric

effects below the steric threshold (the â(θ) term) with a

different steric effect above the steric threshold (the â′(θ -

θ_st) term). If there is no observable steric threshold, then the

“â′(θ - θ_st)” term is set to zero. The presence of so many

variables makes the results from regression analysis ques-

tionable, especially in the detection of a meaningful value

for the steric threshold. Keeping in mind this difficulty, very

recently Giering, Prock et al.²⁸proposed a combined method

of graphical and regression analysis of ligand effect data,

based essentially on the use of data obtained from graphical

analysis to control the results of the regression analysis. This

protocol has been applied to the NMR and kinetic data in

Table 3.

“Graphical” Analysis of the Kinetic Data. A good

estimate of R can be obtained from the plot of ∆G^qvs ø for

the isosteric P(p-XC₆H₄)₃ligands as shown in Figure 8.

Since the parameters θ ) 145° and E_ar) 2.7 are both

constant for this ligand set (compounds 1-6), the variation

in the ∆G^qvalues should reflect the sensitivity of the system

to ligand σ basicity only. In practice, the slope of this plot

(R ) -0.435 ( 0.04 kJ mol^-1cm, r²) 0.981, 6 data points)

affords a fast estimate of the coefficient of ø for the full set

of data in the QALE equation. There is an inhibitory

electronic effect on the rates since the activation energy for

the fluxional motion of Me₂-phen is enhanced as the

phosphanes become better electron donors (smaller ø). The

(17) Bartik, T.; Himmler, T.; Schulte, H. G.; Seevogel, K. J. Organomet.

Chem. 1984, 272, 29-41.

(18) A value of ø for a ligand L is obtained from the difference between

the A₁carbonyl stretching frequency (ν_COin units of cm^-1) for LNi-

(CO)₃and the constant value, 2056.1 cm^-1

.

(19) Tolman, C. A. Chem. Rev. 1977, 77, 313-348.

(20) (a) Seligson, A. L.; Trogler, W. C. J. Am. Chem. Soc. 1991, 113, 2520-

2527. (b) Imyatov, N. S. Koord. Khim. 1985, 11, 1041, 1171-

1178.

(21) (a) Alyea, E. C.; Dias, S. A.; Ferguson, G.; Restivo, R. J. Inorg. Chem.

1977, 16, 2329-2334. (b) Ferguson, G.; Roberts, P. J.; Alyea, E. C.;

Khan, M. Inorg. Chem. 1978, 17, 2965-2967. (c) Alyea, E. C.; Dias,

S. A.; Ferguson, G.; Parvez, M. Inorg. Chim. Acta 1979, 37, 45-52.

(d) Immirzi, A.; Musco, A. Inorg. Chim. Acta 1977, 25, L41-L42.

(e) Porzio, W.; Musco, A.; Immirzi, A. Inorg. Chem. 1980, 19, 2537-

2540. (f) Mu¨ller, T. E.; Mingos, D. M. P. Transition Met. Chem. 1995,

20, 533-539. (g) Smith, J. M.; Coville, N. J. Organometallics 2001,

20, 1210-1215. (h) Smith, J. M.; Coville, N. J.; Cooke, L. M.;

Boeyens, J. C. A. Organometallics 2000, 19, 5273-5280.

(22) (a) Caffrey, M. L.; Brown, T. L. Inorg. Chem. 1991, 30, 3907-3914.

(b) Brown, T. L. Inorg. Chem. 1992, 31, 1286-1294. (c) Brown, T.

L.; Lee, K. J. Coord. Chem. ReV. 1993, 128, 89-116. (d) Choi, M.

G.; Brown, T. L. Inorg. Chem. 1993, 32, 1548-1553.

(23) Liu, H.-Y.; Eriks, K.; Prock, A.; Giering, W. P. Organometallics 1990,

9, 1758-1766.

(24) (a) Wilson, M. R.; Woska, D. C.; Prock, A.; Giering, W. P.

Organometallics 1993, 12, 1742-1752. (b) Farrar, D. H.; Hao, J.;

Poe¨, A. J.; Stromnova, T. A. Organometallics 1997, 16, 2827-2832.

(25) (a) Panek, J.; Prock, A.; Eriks, K.; Giering, W. P. Organometallics

1990, 9, 2175-2176. (b) Lorsbach, B. A.; Prock, A.; Giering, W. P.

Organometallics 1995, 14, 1694-1699.

(26) Fernandez, A. L.; Prock, A.; Giering, W. P. Organometallics 1994,

13, 2767-2772.

(27) (a) Tracey, A. A.; Eriks, K.; Prock, A.; Giering, W. P. Organometallics

1990, 9, 1399-1405. (b) Fernandez, A. L.; Prock, A.; Giering, W. P.

Organometallics 1996, 15, 2784-2789.

(28) Bartholomew, J.; Fernandez, A. L.; Lorsbach, B. A.; Wilson, M. R.;

Prock, A.; Giering, W. P. Organometallics 1996, 15, 295-301.

1254 Inorganic Chemistry, Vol. 44, No. 5, 2005

2,9-Dimethyl-1,10-Phenanthroline in Platinum(II) Complexes

considered an outlier. The exclusion of PCy(C₆H₅)₂increased

significantly the quality of the fit, but it appeared that the

contribution of the parameter â was statistically insignificant.

Accordingly, it was dropped from the analysis, and the datum

for PCy(C₆H₅)₂was removed from the data set. The resulting

regression equation is

∆G^q) (70.6 ( 3) + (-0.43 ( 0.04)(ø) -

(0.47 ( 0.05)(θ - 148°)λ + (2.2 ( 0.3)(E_ar)

(data points ) 12, DC ) 0.997, MSC ) 4.27)

(3)

that corresponds to steric and electronic contributions of 38

and 40%, respectively, and of about 22% for the aryl

contribution.³⁰As a measure of goodness-of-fit, we use the

coefficient of determination DC ) 0.997 and the value of

MSC ) 4.918 (model selection criterion).³¹An appropriate

index of goodness-of-fit is also given by the correspondence

between the values of R (-0.425 ( 0.04 kJ mol^-1cm)

obtained from full regression analysis and the value of R

(-0.435 ( 0.04 kJ mol^-1cm) obtained from the plot of ∆G^q

vs ø for the isosteric ligands P(4-XC₆H₄)₃, where θ and E_ar

remain constant (Figure 8). There is also an excellent

correspondence between the values of γ from full regression

(γ ) 2.23 ( 0.3 kJ mol^-1) and the value resulting from the

graphical analysis (γ ) 2.22 kJ mol^-1). The values of ∆G^q

calculated using the regression coefficients in eq 3 are

included in Table 3. A significant deviation from the

experimental data is observed only for PCy(C₆H₅)₂, which

we have treated as an “outlier”.

Stereoelectronic Analysis of ¹J_PtPCoupling Constants.

The values of ¹J_PtPcoupling constants of the complexes 1-14

in Table 3 were analyzed with eq 2, setting apart the value

for complex 13 and using the values of ø, θ, and E_aras

stereoelectronic parameters of the ligands. The QALE

analysis has been performed according to the protocol

described above for the kinetic data and led to the equation:

Figure 8. Plot of ∆G^qvs ø for isosteric triaryl P-donor ligands (1-6,

empty squares) and trialkyl P-donor ligands (9-11, 14, filled squares).

data for three of the trialkyl phosphanes 10, 11, 14 fit a

reasonably good straight line with a positive slope that

intersects the previous line at a value of ø close to 8.2. These

observations allow for two main conclusions to be drawn:

(i) there is a dominant steric effect associated with the trialkyl

P-donor ligands that operates in opposite direction to the

σ-donor effect (otherwise the two sets of data would lie on

the same line), and (ii) there is a significant aryl effect. In

the absence of an aryl effect, the two lines would have

intersected at a value of ø ) 4.7, corresponding to the basicity

of an hypothetical trialkyl ligand with a cone angle of 145°,

the same as those of the triarylphosphanes. The magnitude

of the deviation is a measure of the aryl effect. The

experimental line for the triarylphosphanes (1-6) lies almost

6 kJ mol^-1above a parallel imaginary line intersecting the

trialkylphosphane line at ø ) 4.7, which suggests that the

aryl effect operates in the same direction as the electron σ

donation, increasing ∆G^qand leading to a pronounced

decrease in the rates. Since the value of E_ar) 2.7 for the

triarylphosphanes, the value expected for γ in eq 2 is 6/2.7

) 2.22 kJ mol^-1.

In the search for a steric threshold, we found that a plot

of ∆G^qvs “i” (where “i” represents the number of aryl groups

of a component of the family of the mixed alkyl-arylphos-

phane) was perfectly linear (slope ) 1.29 ( 0.09 kJ mol^-1,

r²) 0.995, 4 data points), thus suggesting the absence of a

steric threshold at least until the value of the cone angle of

the most sterically hindered ligand (PPh₃, θ ) 145°).

However, the steric profile constructed on plotting the values

of ∆G^qvs θ for the alkyl phosphanes (9-11, 14) suggested

the presence of a steric threshold in the cone angle range of

147-149°.

¹J_PtP) (3745 ( 54) + (10.3 ( 1)(ø) + (3.9 ( 0.4)(θ) +

(-5.5 ( 1)(θ - 150)λ + (51 ( 5) (E_ar)

(data points ) 13, DC ) 0.997, MSC ) 5.07)

(4)

At variance with the results of the analysis performed on

the kinetic data, for the NMR data the â(θ) term of eq 2 is

statistically significant, indicating that there is a nonzero

positive steric effect below the steric threshold. The values

1

of J_PtPcalculated using the regression coefficients in eq 4

are included in Table 3. A significant deviation from the

Regression Analysis of the Kinetic Data. A regression

analysis provides a more accurate evaluation of the single

contributions of the stereoelectronic parameters to the

activation energy of the Me₂-phen flipping. The graphical

analysis suggests that eq 2 is suitable to analyze the energy

data in Table 3 since it accounts for steric (θ) and electronic

(σ + E_ar) effects as well as for the presence of a steric

threshold. The results of the first regression analysis of all

data points (n ) 13), performed using eq 2 and the

SCIENTIST program,²⁹revealed that PCy(C₆H₅)₂must be

(30) A useful way to display the extent to which a parameter affects a

property is to calculate the percentage contribution of that parameter

using the regression coefficients derived from eq 3 and defining the

maximum range of variation of the parameters (∆ø ) 26 cm^-1; ∆θ

) 22°; ∆E_ar) 2.7), according to the equation: %ø ) 100(|R| ∆ø)/

[(|R| ∆ø) + (|â| ∆θ) + (|γ|∆E_ar)].

(31) The coefficient of determination DC measures the fraction of the total

variance accounted for by the model. When dealing with a multiplicity

of possible models, a more appropriate index of goodness-of-fit is

the MSC (model selection criterion). The most appropriate model will

be that with the largest MSC. A supplementary statistical criterion is

given by the value of r²) 0.994 for the linear plot of ∆G^q

vs

(calc)

∆G^q_(obs), where ∆G^q

is obtained by introducing the calculated

(calc)

(29) SCIENTIST; Micro Math Scientific Software: Salt Lake City, UT.

coefficients in eq 3.

Inorganic Chemistry, Vol. 44, No. 5, 2005 1255

Romeo et al.

interest to reiterate that the aryl effect has a significant

positive effect on both the properties analyzed (the regression

coefficients γ(E_ar) are both positive 2.23 kJ mol^-1and 50.5

1

Hz for ∆G^qand J_PtP, respectively). The electronic profile

in Figure 9A indicates that the activation energy for the

fluxional motion of Me₂-phen in the complexes is enhanced

as the phosphanes become better electron donors (smaller

ø, R ) -0.425 ( 0.04 kJ mol^-1cm).

In contrast, the values of ¹J_PtPcoupling constants decrease

linearly with increasing electron donation by the P-donor

ligands, as indicated by the electronic profile in Figure 10A.

The two steric profiles exhibit well-defined steric thresholds

1

at 150° for J_PtP(Figure 10B) and at 148° for ∆G^q(Figure

9B), the only difference being that along the set of small

ligands (characterized by values of cone angle θ < θ_st), the

coupling constants ¹J_PtPincrease before the onset of the steric

threshold, while the same set of ligands does not affect

significantly the activation energy ∆G^qof the flipping.

Bonding of Phosphanes to Platinum by NMR. Coupling

1

Figure 9. Electronic profile (upper plot) and steric profile (lower plot)

for the free activation energy of the fluxional motion of Me₂-phen in [PtMe-

(Me₂-phen)(PR₃)]⁺. Open squares refer to complexes containing triaryl P(4-

XC₆H₄)₃phosphanes.

constants J_PtPof closely related planar platinum(II) com-

plexes can be regarded as a good diagnostic probe of the

changes in 6s character of the hybrid orbital of platinum used

in bonding to the phosphorus atom.³³Smaller values of ¹J_PtP

correspond to longer Pt-P bond distances and to higher trans

influences of groups in trans position to the bond.³⁴We have

summarized in Table 4 the results of the QALE analysis

1

carried out on J_PtPof complexes 1-14 (coefficients and

statistics), together with similar regression analysis of data

for other platinum(II) complexes taken from the recent

literature.

The value of R (10.3 ( 1 Hz cm), which represents the

1

sensitivity of J_PtPof [Pt(Me)(Me₂-phen)(PR₃)]⁺to the

inductive effects brought about by substituents on phospho-

rus, is comparable to that of other cationic complexes having

the same N-Pt-P bond axis as that for [Pt(N-N-C)(PR₃)]⁺

(N-N-CH ) 6-(1-methylbenzyl)-2.2′-bipyridine, R ) 14.1

( 3 Hz cm),³⁵or the same P-Pt-P bond axis as that for

trans-[Pt(PR₃)₂Me(CH₃OH)]⁺³⁶(R ) 14.6 ( 2 Hz cm) and

trans-[Pt(PR₃)₂MeCl]³⁷(R ) 11.3 ( 0.5 Hz cm). In contrast,

for uncharged complexes of cis geometry having either strong

or weak trans-activating groups, ¹J_PtPincreases on increasing

the electron-donor ability of the substituent on the phosphorus

ligand. The values of R (Hz cm) are -8.5 ( 0.7 for cis-

[PtPh₂(CO)(PR₃)],³⁸-6 ( 1 for cis-[PtMe₂(PR₃)₂],³⁶-7.2

( 0.8 for cis-[PtMe₂(PR₃)(Me₂SO)],³⁹-8.1 ( 0.9 for cis-

[PtMe₂(PR₃)(py)],³⁹and -8.9 ( 0.3 for cis-[Pt(PR₃)₂Cl₂].³⁷

For cis-[Pt(PR₃)₂MeCl],³⁷R is -3.4 ( 0.3 with PR₃trans to

Figure 10. Electronic profile (upper plot) and steric profile (lower plot)

1

for the J_PtPvalues of [PtMe(Me₂-phen)(PR₃)]⁺complexes.

experimental data is observed only for PCy₂(C₆H₅), which

we have considered as an “outlier” in the QALE analysis.

Stereolectronic Profiles. The results of the QALE analysis

can now be displayed as electronic, steric, and E_arprofiles

(Figures 9 and 10).

These plots were constructed by subtracting from the

experimental data the contributions of all the terms of the

regression eqs 3 and 4, except that of the variable of interest,

(i.e., R(ø) in the electronic profiles).³²For the sake of space,

the aryl profiles are omitted in Figures 9 and 10, but it is of

(33) Allen, F. H.; Pidcock, A. J. Chem. Soc. A 1968, 2700-2704.

(34) (a) Appleton, T. G.; Clark, H. C.; Manzer, L. E. Coord. Chem. ReV.

1973, 10, 335-422. (b) Appleton, T. G.; Bennett, M. A. Inorg. Chem.

1978, 17, 738-747. (c) Grim, S. O.; Keiter, R. L.; McFarlane, W.

Inorg. Chem. 1967, 6, 1133-1137. (d) Allen, F. H.; Sze, S. N. J.

Chem. Soc. A 1971, 2054-2056.

(35) Romeo, R.; Plutino, M. R.; Monsu` Scolaro, L.; Stoccoro, S. Inorg.

Chim. Acta 1997, 265, 225-233.

(36) Romeo, R.; Alibrandi, G. Inorg. Chem. 1997, 36, 4822-4830.

(37) Cobley, C. J.; Pringle, P. Inorg. Chim. Acta 1997, 265, 107-115.

(38) Romeo, R.; Arena, G.; Monsu` Scolaro, L. Inorg. Chem 1994, 33,

4029-4037.

(32) As an example, the electronic profile in the upper plot of Figure 9

was constructed according to the equation ∆G^q(ø) ) ∆G^q_(obsd)- (â′-

(θ - θ_st)λ + γ (E_ar)).

(39) Romeo, R.; Monsu` Scolaro, L.; Plutino, M. R.; Fabrizi de Biani, F.;

Bottari, G.; Romeo, A. Inorg. Chim. Acta 2003, 350, 143-151.

1256 Inorganic Chemistry, Vol. 44, No. 5, 2005

2,9-Dimethyl-1,10-Phenanthroline in Platinum(II) Complexes

1

Table 4. Selected Coefficients Derived from QALE Analysis for J_PtPof Some Platinum(II) Complexes

R

â

â′

γ

ω

complexes

n^a

Hz cm

Hz deg^-1

Hz

θ

_stdeg

150

DC^b

MSC^c

ref

[Pt(Me)(dmphen)(PR₃)]⁺

[Pt(N-N-C)(PR₃)]⁺

trans-[Pt(Me)(PR₃)₂(MeOH)]⁺

trans-[PtMeCl(PR₃)₂]^d

cis-[Pt(Ph)₂(CO)(PR₃)]

cis-[Pt(Me)₂(PR₃)₂]

13

14

13

6

10

13

6

10.3( 1

14.1 ( 3

14.6 ( 2

3.91 ( 0.4

4.1 ( 0.6

3.6 ( 0.6

-5.5 ( 1

-3.7 ( 1

51 ( 6

43 ( 10

64 ( 7

3745 ( 54

3515 ( 90

2240 ( 62

2989 ( 7

2480 ( 50

1338 ( 58

2001 ( 10

2053 ( 10

3796 ( 4

4543 ( 4

1868 ( 10

0.997

0.975

0.997

0.993

0.973

0.985

0.958

0.949

0.995

0.981

0.986

5.07

3.11

4.98

4.30

3.01

3.45

2.49

2.31

4.60

3.16

3.45

this work

35

<122

151

36

37

38

36

39

37

11.3 ( 0.5

-8.5 ( 0.7

-6.0 ( 1

-7.2 ( 0.8

-8.1 ( 0.9

-8.9 ( 0.3

-3.4 ( 0.3

-10.5 ( 0.7

-4.9 ( 0.3

4.0 ( 0.4

<122

-8.9 ( 1

24 ( 5

149

cis-[Pt(Me)₂(PR₃)(Me₂SO)]^d

cis-[Pt(Me)₂(PR₃)(py)]^d

cis-[PtCl₂(PR₃)₂]^d

6

cis-[PtMeCl(PR₃)₂]^d

5^e

5^f

e

1

^aNumber of data points. ^bCoefficient of determination. ^cModel selection criterion. ^dRegression analysis relative to isosteric phosphanes only. J_PtPfor

f

1

PR₃trans to chloride. J_PtPfor PR₃trans to methyl group.

chloride, -10.5 ( 0.7 with PR₃trans to the methyl group.

Setting apart a comparison among the trans complexes, which

is complicated by the fact that the ligand trans to PR₃is

another PR₃that is different in each complex, it would seem

that for uncharged species, the more electron withdrawing

the substituent the smaller the ¹J_PtP, while for cationic species

the effect is opposite. This latter behavior corresponds to

that of electron-rich platinum(0) complexes that has been

rationalized on the basis of π-bonding effects.³⁷Electron

withdrawing should favor the metal-to-phosphorus π ac-

ceptance and involve a synergistic increase of the phosphorus-

to-metal σ donation, which strengthens the bond and is

distances.⁴⁵Under these circumstances, steric repulsion

prevents maximum overlap of phosphorus- and platinum-

bonding orbitals and changes the s character present in the

metal-phosphorus bond. Thus, the steric threshold in the

1

plot of J_PtPvs the cone angles (Figure 10B), and the sharp

change in the direction of the steric effects at 150°, can be

assumed as a signal that marks the onset of significant

changes in the structure of the [Pt(Me)(Me₂-phen)(PR₃)]⁺

complexes. This behavior is analogous to that found for cis-

[Pt(PR₃)₂Me₂] complexes³⁶and has been confirmed recently

by Nolan et al.⁴⁶by determining the reaction enthalpies of a

variety of such complexes and the X-ray molecular structures

when PR₃) PEt₃, PMe₂Ph, P(pyrrolyl)₃, and PCy₃. The

relative stability of the dimethyl-bisphosphane platinum(II)

complexes was found to be strongly influenced by the size

of the phosphane, with larger cone angles resulting in less

thermodynamically stable complexes. For instance, cis-[Pt-

(PCy₃)₂Me₂] (PCy₃, θ )170°) has the lowest value of

enthalpy of formation (-∆H ) 19.2 kcal/mol), the longer

Pt-P bond separation (2.344(1) Å), and the largest P-Pt-P

bond angle (P₁-Pt-P₂) 108.60(5)°).

1

37

accompanied by an increase in J_PtP

.

This explanation

clearly does not apply to cationic platinum(II) species, and

in addition, an essential tenet of the QALE analysis is that

π effects are absent in alkyl- and arylphosphanes P(4-

XC₆H₄)₃used as P-donor ligands.

A rationale for the pattern of behavior exhibited by the

dependencies of the NMR data is not straightforward since

the direction and the extent of stereoelectronic effects on

1

the value of J_PtPcoupling constants appear to depend on

the nature of groups attached to phosphorus,⁴⁰the trans

activating group,³⁴the chelate ring size,⁴¹the platinum

oxidation state,⁴²the platinum-phosphorus bond length,⁴³

and as seen above, by the geometry and charge of the

complex. Perhaps we would limit the interpretation of the

¹J_PtPelectronic profiles to the simple observation of whether

electron donation from substituents increases the covalent

character and the strength of the Pt-P bond.

Potential Energy Surface and Flipping Mechanism. The

stereoelectronic analysis of the coupling constants J_PtPfor

1

1-14 has shown that there is an efficient flow of charge

density along the P-Pt-N axis on changing the basicity (ø

values) of the coordinated phosphane. This electron flow also

affects the individual rates of the various complexes, as

shown by the linear correlation of the free energy of

activation ∆G^qwith ø in Figure 9A. However, the steric plot

in Figure 9B, which describes the steric dependence of the

free activation energies of these reactions and the sensitivity

of the Me₂-phen flipping to steric effects, is particularly

diagnostic in assessing the flipping mechanism. The shape

of the steric plot is that expected for a purely dissociative

process⁴⁷and has been found in a number of dissociative

substitutions on carbonyl compounds.⁴⁸The steric depen-

dence is the result of the different response of the energy of

Steric effects also play a significant role.^36,44Above the

steric threshold, the overload of steric congestion leads to a

1

sharp decrease of J_PtPthat must be associated with severe

distortions of the bond angles and lengthening of Pt-P bond

(40) Pregosin, P. S.; Kunz, R. W. In ³¹P and ¹³C NMR of Transition Metal

Complexes; Diehl, P., Fluck, E., Kosfeld, R., Eds.; Springer: New

York, 1979.

(41) Garrou, P. E. Inorg. Chem. 1975, 14, 1435-1439.

(42) Pregosin, P. S. Phosphorus-31 NMR Spectroscopy in Stereochemical

Analysis. In Organic Compounds and Metal Complexes; Verkade, J.

G., Quin, L. D., Eds.; VCH: New York, 1987; Chapter13 and

references therein.

(45) (a) Clark, H. C.; Hampden-Smith, M. J. Coord. Chem. ReV. 1987, 79,

229-255 and references therein. (b) Immirzi, A.; Musco, A.; Mann,

B. E. Inorg. Chim. Acta 1977, 21, L37-L38. (c) Clark, H. C.;

Nicholas, A.; Martin de P. Magn. Reson. Chem. 1990, 28, 99-103.

(46) Haar, C. M.; Nolan, P. S.; Marshall, W. J.; Moloy, K. G.; Prock, A.;

Giering, W. P. Organometallics 1999, 18, 474-479.

(43) (a) Mather, G. G.; Pidcock, A.; Rapsey, G. J. N. J. Chem. Soc., Dalton

Trans. 1973, 2095-2099. (b) Crispini, A.; Harrison, K. N.; Orpen,

A. G.; Pringle, P. G.; Wheatcroft, J. R. J. Chem. Soc., Dalton Trans.

1996, 1069-1076.

(47) Ericks, K.; Giering, W. P.; Liu, H. Y.; Prock, A. Inorg. Chem. 1989,

28, 1759-1763.

(44) Romeo, R. Comments Inorg. Chem. 2002, 23, 79-100.

Inorganic Chemistry, Vol. 44, No. 5, 2005 1257

Romeo et al.

Chart 2

Figure 11. Free energy surface calculated for all possible combinations

of ø and θ. The spikes account for the contribution from E_ar.

the ground and the transition states to changes in the size of

the “spectator” ligands. The first horizontal upper part, for

the ligands that fall before the steric threshold (θ < θ_ster),

limits a region where steric effects are not operative both in

the ground and in the transition state. The value of the steric

threshold (θ_ster) 148°) is almost coincident with that derived

photochemical activation⁴⁹or in a rare case in which the

molecule already has a strong tetrahedral distortion in the

ground state, as reported recently for the fluxional behavior

of cis-bis(silyl)bis(phosphane)platinum(II).⁵⁰The process

features an uncatalyzed isomerization, many examples of

which can be found in the literature.³⁶The interconversion

of two η¹-coordinate three-coordinate species is also dem-

onstrated for the dynamic behavior of bidentate nitrogen

ligands in some palladium(II) complexes.⁵¹

1

from the J_PtPanalysis (θ_ster) 150°) and, as in the latter,

marks the onset of steric destabilization of the ground state.

In contrast, in bimolecular associative processes, when steric

effects come into play, they are operative through a continu-

ous destabilization of the transition state.^35-38

A free-energy surface representing the general σ basicity

and steric effects in a dissociative process is shown in Figure

11 and has been constructed using the results from regression

analysis (eq 2), according to a method recently proposed by

Poe¨ et al.^15d,52for associative reactions of metal-carbonyl

clusters. This type of plot predicts the way in which a

P-donor ligand should affect the energy of the transition state

in the absence of aryl or π-acidity effects. The spikes indicate

the additional contribution due to the aryl effect for some

phosphorus ligands.

There is significant release of steric strain if one arm of

the Me₂-phen ligand dissociates from the highly congested

four-coordinate [Pt(Me)(Me₂-phen)(PR₃)]⁺compounds to a

more flexible three-coordinate T-shaped intermediate. A

dissociative mechanism, such as that illustrated in Chart 2,

involves (i) platinum-nitrogen bond breaking and the

formation of the two T-shaped intermediates I₁and I₃, (ii)

their isomerization into the corresponding intermediates I₂

and I₄, and (iii) finally, ring closing. In any event there is

another flip possible, one which keeps the N atoms attached

in the same location but interconverts enantiomers. This

apparently occurs at lower temperatures since the potentially

diastereotopic methyls in phosphane 8 are equivalent. Hence,

there is presumably Pt-N bond breaking occurring rapidly

at low temperature, but the “flipping” observed at the higher

temperature is really associated with the T-shaped intermedi-

ate, allowing the monohapto complex to shift the single bond

from trans to P to trans to Me (I₁to I₂). The mechanism has

already been proposed for the fluxional motion of Me₂-phen

when PR₃) P(C₆H₅)₃,¹and applies to all the series of related

compounds in view of the absence of potential reagents and

considering that the solvent or the BArf counterion is too

weakly coordinating to promote a nucleophilic attack and

reaction pathways via five-coordinate species. An alternative

intramolecular twist rotation pathway is accessible only to

Conclusions

The severe distortion of the bidentate nitrogen ligand 2,9-

dimethyl-1,10-phenanthroline in alkyl platinum(II) complexes

of the type [Pt(Me)(Me₂-phen)(PR₃)]⁺and the lengthening

of the Pt-N bonds are at the origin of its fluxional motion

1

between different exchanging sites. The J_PtPcoupling

(49) (a) Whitesides, T. H. J. Am. Chem. Soc. 1969, 91, 2395-2396. (b)

Costanzo, L. L.; Giuffrida, S.; Romeo, R. Inorg. Chim. Acta 1980,

38, 31-35. (c) Price, J. H.; Birk, J. P.; Wayland, B. B. Inorg. Chem.

1978, 17, 2245-2250.

(50) (a) Tsuji, Y.; Nishiyama, K.; Hori, S.-Y.; Ebihara, M.; Kawamura, T.

Organometallics 1998, 17, 507-512. (b) Obora, Y.; Tsuji, Y.;

Nishiyama, K.; Ebihara, M.; Kawamura, T. J. Am. Chem. Soc. 1996,

118, 10922-10923.

(51) (a) Albinati, A.; Kunz, R. W.; Ammann, C. J.; Pregosin, P. S.

Organometallics 1991, 10, 1800-1806. (b) Gogoll, A.; Ornebro, J.;

Grennberg, H.; Bakwall, J. E. J. Am. Chem. Soc. 1994, 116, 3631-

3632. (c) Delis, J. G. P.; Aubel, P. G.; Vrieze, K.; van Leeuwen, P.

W. N. M.; Veldman, N.; Spek, A. L.; van Neer, F. J. R. Organome-

tallics 1997, 16, 2948-2957.

(48) (a) Babij, C.; Chen, L.; Koshevoy, I. O.; Poe¨, A. J. J. Chem Soc.,

Dalton Trans. 2004, 833-838. (b) Chalk, K. L.; Pomeroy, R. K. Inorg.

Chem. 1984, 23, 444-449. (c) Chen, L.; Poe¨, A. J. Inorg. Chem. 1989,

28, 3641-3647. (d) Brodie, N. M. J.; Poe¨, A. J. Can. J. Chem. 1995,

73, 1187-1195.

(52) Bunte, K. A.; Farra, D. H.; Poe¨, A. J. Organometallics 2003, 22, 3448-

3454.

1258 Inorganic Chemistry, Vol. 44, No. 5, 2005

2,9-Dimethyl-1,10-Phenanthroline in Platinum(II) Complexes

Synthesis of Complexes. The complex trans-[Pt(Cl)(Me)(Me₂-

SO)₂] was prepared according to Eaborn et al.⁵⁵and was purified

by several crystallizations from dichloromethane/diethyl ether

mixtures. The complexes [Pt(Me)(Me₂-phen)(Me₂SO)]PF₆and [Pt-

(Me)(Me₂-phen)(P(C₆H₅)₃)]PF₆were prepared following published

procedures.¹The complexes [Pt(Me)(Me₂-phen)(P)]BArf (P )

P(C₆H₅)₃1, P(4-FC₆H₄)₃2, P(4-ClC₆H₄)₃3, P(4-CF₃C₆H₄)₃4, P(4-

MeOC₆H₄)₃5, P(4-MeC₆H₄)₃6, PMe(C₆H₅)₂7, PMe₂(C₆H₅) 8,

PMe₃9, PEt₃10, P(i-Pr)₃11, PCy(C₆H₅)₂12, PCy₂(C₆H₅) 13, and

PCy₃14) were prepared by using essentially the method described

below for compound 3.

constants of the complexes and the free activation energies

for the flipping have been analyzed quantitatively, according

to steric and electronic properties of the P-donor ligands by

the QALE method. The results of the analysis on NMR and

kinetic data are corroborated by the results of the structural

studies, indicating that phosphorus ligands with cone angles

greater than 150° cause an overload of steric congestion in

the ground state. This remarkable steric congestion at the

coordination plane favors the facile dissociation of the Pt-N

bonds and the formation of a T-shaped η¹-ring-opened three-

coordinate species whose fluxionality accounts for the

dynamic behavior of the bidentate nitrogen ligand. The free-

energy surface constructed with the results of the QALE

analysis on the kinetic data gives a simple widespread

graphical representation of the σ basicity and steric effects

upon which the aryl effects are separately superimposed as

additional peaks.

[Pt(Me)(Me₂-phen)(P(4-ClC₆H₄)₃)]BArf, 3. A dichloromethane

solution (20 mL) of P(4-ClC₆H₄)₃(118.4 mg, 0.324 mmol) was

added dropwise under continuous stirring to a solution (20 mL) of

[Pt(Me)(Me₂-phen)(Me₂SO)]PF₆(207.8 mg, 0.324 mmol). Evapora-

tion of most of the solvent, addition of diethyl ether, and cooling

to -30 °C led to the separation of a powdery solid of [Pt(Me)-

(Me₂-phen)(P(4-ClC₆H₄)₃)]PF₆3a (87.5% yield). This latter was

dissolved again in dichloromethane, and the stoichiometric amount

of Na[B(3,5-(CF₃)₂C₆H₃)₄] (251.6 mg, 0.284 mmol) was added. The

white solid (NaPF₆) formed under stirring was filtered off, and

evaporation of the solvent led to the formation of 3 (91% yield) as

a brown solid.

Experimental Section

General Procedures and Chemicals. All syntheses were

performed under a dry, oxygen-free nitrogen atmosphere using

standard Schlenk-tube techniques or in a glovebox containing less

than 1 ppm of oxygen and water; however, the products may be

worked up and handled in air. All solvents were analytical reagent

grade (Lab-Scan Ltd) and were used in the synthetic procedures

after distillation under a nitrogen atmosphere from appropriate

drying agents: diethyl ether from sodium benzophenone ketyl,

dichloromethane from barium oxide, dimethylsulfoxide, at low

pressure, from CaH₂, after preliminary filtration through an alumina

column. All solvents were stored in N₂-filled flasks over activated

4-Å molecular sieves. Chloroform-d (99.96+%, C. I. L. Inc.) was

dried standing for many days over CaH₂, distilled under nitrogen

over activated magnesium sulfate and sodium carbonate, and then

stored over activated 4-Å molecular sieves. K₂PtCl₄(Strem) was

purified by dissolving it in water and filtering. The salt Na[B(3,5-

(CF₃)₂C₆H₃)₄] was prepared according to the literature method.⁵³

All phosphane ligands used in these studies were purchased from

Strem or Aldrich. Solid phosphanes were recrystallyzed from EtOH

by dissolving in the hot solvent, filtering, and cooling the filtrate

to 0 °C. The crystals were stored and used under nitrogen. All the

other chemicals were the highest grade commercially available and

were used as received.

[Pt(Me)(Me₂-phen)(P(C₆H₅)₃)]BArf, 1: ¹H NMR (CDCl₃, T

) 260 K): δ 8.32 (d, ³J_HH) 8.3 Hz, 1H, H₄), 8.15 (d, ³J_HH) 8.4

Hz, 1H, H₇), 7.75 (AB system, ³J_HH) 8.9 Hz, 1H, H₅), 7.73 (AB

system, ³J_HH) 8.9 Hz, 1H, H₆), 7.73 (m, 8H, H_o,o′-BArf), 7.68 (d,

5

3

³J_HH) 8.5 Hz, J_PH) 1.3 Hz, 1H, H₃), 7.52 (d, J_HH) 8.3 Hz,

³J_PH) 10.5 Hz, 6H, H_o,o′-P), 7.52 (buried under H_o,o′-P, 3H, H_p-

P), 7.48 (m, br, 4H, H_p-BArf), 7.38 (dd, ³J_HH) 8.3 Hz, ³J_HH) 6.9

Hz, ⁴J_PH) 2.4 Hz, 6H, H_m,m′-P), 7.09 (d, ³J_HH) 8.4 Hz, 1H, H₈),

3.02 (s, 3H, Me_A), 1.90 (s, 3H, Me_B), 0.74 (s, ²J_PtH) 66.9 Hz, ³J_PH

) 4.1 Hz, 3H, Pt-CH₃). ³¹P{¹H} NMR (CDCl₃): δ 14.3 (s, ¹J_PtP

)

4575 Hz). Anal. Calcd for C₆₅H₄₂BF₂₄N₂PPt: C, 50.57; H, 2.74;

N, 1.81. Found: C, 50.71; H, 2.83; N, 1.85.

[Pt(Me)(Me₂-phen)(P(4-FC₆H₄)₃)]BArf, 2: ¹H NMR (CDCl₃,

3

T ) 260 K): δ 8.32 (d, J_HH) 8.4 Hz, 1H, H₄), 8.21 (d, J_HH

)

8.4 Hz, 1H, H₇), 7.76 (s, 2H, H_5,6), 7.72 (m, br, 8H, H_o,o′-BArf),

7.67 (d, ³J_HH) 8.4 Hz, 1H, H₃), 7.51 (m, 6H, H_o,o′-P), 7.46 (m, br,

4H, H_p-BArf), 7.16 (d, ³J_HH) 8.4 Hz, 1H, H₈), 7.09 (m, 6H, H_m,m′

-

P), 2.99 (s, 3H, Me_A), 1.92 (s, 3H, Me_B), 0.69 (s, ²J_PtH) 74.0 Hz,

³J_PH) 4.4 Hz, 3H, Pt-CH₃). ³¹P NMR (CDCl₃): δ 12.3 (¹J_PtP

)

4618 Hz). Anal. Calcd for C₆₅H₃₉BF₂₇N₂PPt: C, 48.86; H, 2.46;

N, 1.75. Found: C, 48.46; H, 2.95; N, 1.36.

Instrumentation. NMR spectra were recorded on a Bruker AMX

R-300 spectrometer equipped with a broad-band probe operating

[Pt(Me)(Me₂-phen)(P(4-ClC₆H₄)₃)]BArf, 3: ¹H NMR (CDCl₃,

1

at 300.13 and 121.50 MHz for H and ³¹P nuclei, respectively.

3

T ) 260 K): δ 8.33 (d, J_HH) 8.4 Hz, 1H, H₄), 8.26 (d, J_HH

)

Proton chemical shifts are reported in parts per million (δ/ppm)

relative to tetramethylsilane (Me₄Si) as an internal standard (0.0

ppm) or referenced with the proton resonance resulting from

incomplete deuteration of the NMR solvent (CDCl₃: 7.26 ppm).

³¹P{¹H} NMR signals are reported in ppm (δ) relative to external

85% H₃PO₄at 0.0 ppm. Coupling constants are given in hertz (J/

8.4 Hz, 1H, H₇), 7.78 (s, 2H, H_5,6), 7.73 (m, br, 8H, H_o,o′-BArf),

3

7.68 (d, J_HH) 8.4 Hz, 1H, H₃), 7.47 (m, br, 4H, H_p-BArf), 7.40

3

(m, br, 12H, H_o,o′-P + H_m,m′-P), 7.20 (d, J_HH) 8.4 Hz, 1H, H₈),

3.00 (s, 3H, Me_A), 1.95 (s, 3H, Me_B), 0.69 (s, ²J_PtH) 74.4 Hz, ³J_PH

) 4.4, 3H, Pt-CH₃). ³¹P NMR (CDCl₃): δ 13.2 (¹J_PtP) 4622 Hz).

Anal. Calcd for C₆₅H₃₉BCl₃F₂₄N₂PPt: C, 47.40 H, 2.39; N, 1.70.

Found: C, 47.84; H, 2.75; N, 1.64.

1

Hz). Phase-sensitive H 2D-NOESY experiments were performed

with a standard pulse sequence by using a mixing time of 0.6 s.

NMR samples were prepared by dissolving ∼20 mg of compound

in 0.5 mL of CDCl₃. The temperature within the probe was

measured using the methanol or ethylene glycol method.⁵⁴Elemen-

tal analyses were performed by Microanalytical Laboratory, Depart-

ment of Chemistry, University College Dublin, Ireland.

[Pt(Me)(Me₂-phen)(P(4-CF₃C₆H₄)₃)]BArf, 4: ¹H NMR (CDCl₃,

3

T ) 260 K): δ 8.27 (d, J_HH) 8.4 Hz, 1H, H₄), 8.18 (d, J_HH

8.4 Hz, 1H, H₇), 7.69 (m, br, 21H, H₃+ H_o,o′-BArf + H_o,o′-P +

_m,m′-P), 7.63 (s, 2H, H_5,6), 7.43 (m, br, 4H, H_p-BArf), 7.08 (d,

)

H

³J_HH) 8.4 Hz, 1H, H₈), 2.97 (s, 3H, Me_A), 1.86 (s, 3H, Me_B), 0.73

(s, J_PtH) 70.0 Hz, J_PH) 4.4 Hz, 3H, Pt-CH₃). ³¹P NMR

2

3

(53) Brookhart, M.; Grant, B.; Volpe, A. F. Organometallics 1992, 11,

3920-3922.

(54) (a) Van Geet, A. L. Anal. Chem. 1968, 40, 2227-2229. (b) Van Geet,

A. L. Anal. Chem. 1970, 42, 679-680.

(55) Eaborn, C.; Kundu, K.; Pidcock, A. J. Chem. Soc., Dalton Trans. 1981,

933-938.

Inorganic Chemistry, Vol. 44, No. 5, 2005 1259

Romeo et al.

(CDCl₃): δ 15.1 (¹J_PtP) 4656 Hz). Anal. Calcd for C₆₈H₃₉BF₃₃N₂-

PPt: C, 46.73; H, 2.25; N, 1.60. Found: C, 46.22; H, 2.21; N,

1.56.

4327 Hz). Anal. Calcd for C₅₃H₄₂BF₂₄N₂PPt: C, 45.48; H, 3.02;

N, 2.00. Found: C, 44.98 H, 2.93; N, 1.98.

[Pt(Me)(Me₂-phen)(P(i-Pr)₃)]BArf, 11: ¹H NMR (CDCl₃, T

) 255 K): δ, 8.23 (d, ³J_HH) 8.3 Hz, 1H, H₄), 8.22 (d, ³J_HH) 8.3

1

[Pt(Me)(Me₂-phen)(P(4-MeOC₆H₄)₃)]BArf, 5: H NMR (CDCl₃,

3

T ) 260 K): δ 8.32 (d, J_HH) 8.4 Hz, 1H, H₄), 8.18 (d, J_HH

)

Hz, 1H, H₇), 7.72 (m, br, 10H, H_5,6+ H_o,o′-BArf), 7.58 (d, ³J_HH

)

8.4 Hz, 1H, H₇), 7.76 (s, 2H, H_5,6), 7.73 (m, br, 8H, H_o,o′-BArf),

8.3 Hz, 1H, H₃), 7.54 (d, ³J_HH) 8.3 Hz, 1H, H₈), 7.48 (m, br, 4H,

H_p-BArf), 2.94 (s, 3H, Me_A), 2.92 (s, 3H, Me_B), 2.32 (m, 3H,

3

7.67 (d, J_HH) 8.4 Hz, 1H, H₃), 7.49 (m, br, 4H, H_p-BArf), 7.46

3

2

(m, 6H, H_o,o′-P), 7.16 (d, J_HH) 8.4 Hz, 1H, H₈), 6.87 (m, 6H,

P-CHCH₃), 1.04 (m, 18H, P-CHCH₃), 0.96 (s, J_PtH) 73.8 Hz,

H

_m,m′-P), 3.81 (s, 9H, O-CH₃), 3.02 (s, 3H, Me_A), 2.02 (s, 3H, Me_B),

³J_PH) 2.2 Hz, 3H, Pt-CH₃). ³¹P NMR (CDCl₃): δ 23.9 (¹J_PtP

)

0.75 (s, J_PtH) 75.2 Hz, J_PH) 4.4 Hz, 3H, Pt-CH₃). ³¹P NMR

(CDCl₃): δ 9.8 (¹J_PtP) 4561 Hz). Anal. Calcd for C₆₈H₄₈BF₂₄N₂O₃-

PPt: C, 49.99; H, 2.96; N, 1.71. Found: C, 49.65; H, 3.14; N,

1.70.

4358 Hz). Anal. Calcd for C₅₆H₄₈BF₂₄N₂PPt: C, 46.65; H, 3.36;

2

3

N, 1.94. Found: C, 46.58; H, 3.00; N, 1.92.

[Pt(Me)(Me₂-phen)(PCy(C₆H₅)₂)]BArf, 12: ¹H NMR (CDCl₃,

3

T ) 290 K): δ 8.29 (d, J_HH) 8.3 Hz, 1H, H₄), 8.18 (d, J_HH

)

[Pt(Me)(Me₂-phen)(P(4-MeC₆H₄)₃)]BArf, 6: ¹H NMR (CDCl₃,

8.4 Hz, 1H, H₇), 7.72 (s, 2H, H_5,6), 7.73 (m, br, 8H, H_o,o′-BArf),

3

T ) 298 K): δ 8.33 (d, J_HH) 8.3 Hz, 1H, H₄), 8.15 (d, J_HH

)

7.67 (d, J_HH) 8.3 Hz, 1H, H₃), 7.49 (m, br, 4H, H_p-BArf), 7.40

3

8.3 Hz, 1H, H₇), 7.77 (AB system, J_HH) 9.3 Hz, 1H, H₅), 7.75

(m, br, 10H, H_o,o′-P + H_m,m′-P + H_p-P), 7.15 (d, J_HH) 8.4 Hz,

(AB system, ³J_HH) 9.3 Hz, 1H, H₆), 7.70 (m, br, 8H, H_o,o′-BArf),

1H, H₈), 2.98 (s, 3H, Me_A), 2.62 (m, 1H, P-CH), 2.01 (s, 3H, Me_B),

1.91 (m, 2H, C-CH₂), 1.62 (m, 3H, C-CH₂), 1.25 (m, 2H, C-CH₂),

0.95 (s, ²J_PtH) 70.3 Hz, ³J_PH) 3.1 Hz, 3H, Pt-CH₃), 0.88 (m, 3H,

C-CH₂). ³¹P NMR (CDCl₃): δ 13.7 (¹J_PtP) 4501 Hz). Anal. Calcd

for C₆₅H₄₈BF₂₄N₂PPt: C, 50.37; H, 3.12; N, 1.81. Found: C, 50.22;

H, 3.06; N, 1.78.

3

7.67 (d, J_HH) 8.3 Hz, 1H, H₃), 7.47 (m, br, 4H, H_p-BArf), 7.41

(d, J_HH) 8.1 Hz, J_PH) 11.4 Hz, 6H, H_o,o′-P), 7.15 (d, J_HH

3

)

3

8.1 Hz, J_PH) 1.9 Hz, 6H, H_m,m′-P), 7.09 (d, J_HH) 8.3 Hz, 1H,

H₈), 3.02 (s, 3H, Me_A), 2.37 (s, 9H, P-CH₃), 1.95 (s, 3H, Me_B),

0.73 (s, J_PtH) 74.5 Hz, J_PH) 4.2 Hz, 3H, Pt-CH₃). ³¹P NMR

(CDCl₃): δ 12.0 (¹J_PtP) 4557 Hz). Anal. Calcd for C₆₈H₄₈BF₂₄N₂-

PPt: C, 51.50; H, 3.05; N, 1.77. Found: C, 51.65; H, 3.12; N,

1.70.

2

3

[Pt(Me)(Me₂-phen)(PCy₂(C₆H₅))]BArf, 13: ¹H NMR (CDCl₃,

3

T ) 298 K): δ 8.33 (d, J_HH) 8.3 Hz, 1H, H₄), 8.22 (d, J_HH

)

8.3 Hz, 1H, H₇), 7.79 (s, 2H, H_5,6), 7.72 (m, br, 8H, H_o,o′-BArf),

[Pt(Me)(Me₂-phen)(PMe(C₆H₅)₂)]BArf, 7: ¹H NMR (CDCl₃,

7.68 (d, J_HH) 8.3 Hz, 1H, H₃), 7.49 (m, br, 4H, H_p-BArf), 7.44

3

T ) 240 K): δ 8.30 (d, J_HH) 8.3 Hz, 1H, H₄), 8.10 (d, J_HH

)

(dd, ³J_HH) 7.7 Hz, ⁴J_HH) 1.3 Hz, 1H, H_p-P), 7.20 (d, ³J_HH) 7.9

3

8.3 Hz, 1H, H₇), 7.72 (m, br, 10H, H_5,6+ H_o,o′-BArf), 7.64 (d,

³J_HH) 8.3 Hz, 1H, H₃), 7.46 (m, br, 8H, H_p-BArf + H_o,o′-P), 7.37

(m, 6H, H_m,m′-P + H_p-P), 7.03 (d, ³J_HH) 8.3 Hz, 1H, H₈), 3.02 (s,

3H, Me_A), 1.97 (s, 3H, Me_B), 1.94 (s, ³J_PtH) 52.7 Hz, ²J_PH) 10.1

Hz, J_PH) 9.4 Hz, 2H, H_o,o′-P), 7.14 (d, J_HH) 8.3 Hz, 1H, H₈),

3

6.93 (dd, J_av) 7.8 Hz, 2H, H_m,m′-P), 3.03 (s, 3H, Me_A), 2.48 (m,

2H, P-CH), 1.98-1.54 (m, 10H, C-CH₂), 1.85 (s, 3H, Me_B), 1.47-

2

3

1.05 (m, 10H, C-CH₂), 1.03 (s, J_PtH) 72.9 Hz, J_PH) 3.1 Hz,

3H, Pt-CH₃). ³¹P NMR (CDCl₃): δ 11.8 (¹J_PtP) 4287 Hz). Anal.

Calcd for C₆₅H₅₄BF₂₄N₂PPt: C, 50.17; H, 3.50; N, 1.80. Found:

C, 50.30; H, 3.65; N, 1.82.

2

3

Hz, 3H, P-CH₃), 0.90 (s, J_PtH) 72.5 Hz, J_PH) 3.9 Hz, 3H, Pt-

CH₃). ³¹P NMR (CDCl₃): δ -1.0 (¹J_PtP) 4534 Hz). Anal. Calcd

for C₆₀H₄₀BF₂₄N₂PPt: C, 48.63; H, 2.72, N, 1.89. Found: C, 48.75;

H, 2.80; N, 1.82.

[Pt(Me)(Me₂-phen)(P(Cy)₃]BArf, 14: ¹H NMR (CDCl₃, T )

255 K): δ 8.29 (d, ³J_HH) 8.3 Hz, 1H, H₄), 8.25 (d, ³J_HH) 8.3 Hz,

1H, H₇), 7.72 (m, br, 10H, H_5,6+ H_o,o′-BArf), 7.64 (d, ³J_HH) 8.3

[Pt(Me)(Me₂-phen)(PMe₂(C₆H₅))]BArf, 8: ¹H NMR (CDCl₃,

3

T ) 240 K): δ 8.31 (d, J_HH) 8.3 Hz, 1H, H₄), 8.13 (d, J_HH

)

3

8.3 Hz, 1H, H₇), 7.83 (s, 2H, H_5,6), 7.70 (m, br, 8H, H_o,o′-BArf),

Hz, 1H, H₃), 7.59 (d, J_HH) 8.3 Hz, 1H, H₈), 7.48 (m, br, 4H,

7.66 (d, ³J_HH) 8.3 Hz, 1H, H₃), 7.45 (s, br, 4H, H_p-BArf), 7.42-

H_p-BArf), 3.00 (s, 3H, Me_A), 2.93 (s, 3H, Me_B), 2.09 (m, br, 3H,

3

7.22 (m, br, 5H, H_o,o′-P + H_m,m′-P + H_p-P), 7.09 (d, J_HH) 8.3

P-CH), 1.68 (m, br, 12H, C-CH₂), 1.42 (m, br, 6H, C-CH₂), 1.14

Hz, 1H, H₈), 3.02 (s, 3H, Me_A), 2.13 (s, 3H, Me_B), 1.76 (s, ³J_PtH

)

(m, br, 12H, C-CH₂), 0.93 (s, J_PtH) 74.6 Hz, 3H, Pt-CH₃). ³¹P

2

47.4 Hz, J_PH) 10.1 Hz, 6H, P-CH₃), 1.00 (s, J_PtH) 74.2 Hz,

NMR (CDCl₃): δ 13.0 (¹J_PtP) 4315 Hz). Anal. Calcd for C₆₅H₆₀-

BF₂₄N₂PPt: C, 49.98; H, 3.87; N, 1.79. Found: C, 49.85; H, 3.92;

N, 1.82.

³J_PH) 4.4 Hz, 3H, Pt-CH₃). ³¹P NMR (CDCl₃): δ -18.1 (¹J_PtP

)

4379 Hz). Anal. Calcd for C₅₅H₃₈BF₂₄N₂PPt: C, 46.53; H, 2.70;

N, 1.97. Found: C, 46.80; H, 2.73; N, 2.00.

[Pt(Me)(phen)(P(C₆H₅)₃)]PF₆, 15. The complex [Pt(Me)(Cl)-

(phen)] (50 mg, 0.117 mmol) was dissolved in 20 mL of

dichloromethane, and a dichloromethane solution of AgPF₆(29.6

mg, 0.117 mmol) was added dropwise with continuous stirring.

Upon precipitation of AgCl, the color of the solution slowly changed

from yellow to colorless. After filtration of AgCl, the phosphane

was added cautiously (P(C₆H₅)₃, 30.7 mg, 0.117 mmol in 10 mL

of dichloromethane), the solution was filtered on cellulose powder

to remove residual AgCl and concentrated by a rotavapor. n-Hexane

was added, and the mixture was cooled to -35 °C to give 88 mg

of 15 as an off-white solid (yield: 95%).

[Pt(Me)(Me₂-phen)(P(Me)₃)]BArf, 9: ¹H NMR (CDCl₃, T )

270 K): δ 8.31 (d, ³J_HH) 8.3 Hz, 1H, H₄), 8.25 (d, ³J_HH) 8.3 Hz,

3

1H, H₇), 7.75 (AB system, J_HH) 9.2 Hz, 1H, H₅), 7.72 (AB

system, ³J_HH) 9.2 Hz, 1H, H₆), 7.70 (m, br, 8H, H_o,o′-BArf), 7.64

(d, ³J_HH) 8.3 Hz, 1H, H₃), 7.57 (d, ³J_HH) 8.3 Hz, 1H, H₈), 7.47

(m, br, 4H, H_p-BArf), 2.97 (s, 3H, Me_A), 2.91 (s, 3H, Me_B), 1.46

3

2

(s, J_PtH) 45.2 Hz, J_PH) 10.5 Hz, 9H, P-CH₃), 0.92 (s, J_PtH

)

72.9 Hz, J_PH) 4.39 Hz, 3H, Pt-CH₃). ³¹P {¹H} NMR (CDCl₃):

δ -31.8 (¹J_PtP) 4291 Hz). Anal. Calcd for C₅₀H₃₆BF₂₄N₂PPt: C,

44.23; H, 2.67; N, 2.06. Found: C, 43.97; H, 2.37; N, 1.99.

[Pt(Me)(Me₂-phen)(P(Et)₃)]BArf, 10: ¹H NMR (CDCl₃, T )

220 K): δ 8.25 (d, ³J_HH) 8.3 Hz, 1H, H₄), 8.18 (d, ³J_HH) 8.3 Hz,

1H, H₇), 7.74 (m, br, 8H, H_o,o′-BArf), 7.69 (AB system, ³J_HH) 9.7

3

¹H NMR (CDCl₃, T ) 298 K): δ 9.33 (dd, J_PtH) 35.2 Hz,

4

³J_HH) 5.5 Hz, J_HH) 1.1 Hz, J_PH) 3.8 Hz, 1H, H₂), 8.88 (dd,

4

3

³J_HH) 8.2 Hz, J_HH) 1.1 Hz, 1H, H₄), 8.68 (dd, J_HH) 8.2 Hz,

3

Hz, 1H, H₅), 7.67 (AB system, J_HH) 9.7 Hz, 1H, H₆), 7.61 (d,

⁴J_HH) 1.1 Hz, 1H, H₇), 8.18 (dd, J_HH) 5.5, 8.2 Hz, 1H, H₃),

³J_HH) 8.3 Hz, 1H, H₃), 7.53 (d, ³J_HH) 8.3 Hz, 1H, H₈), 7.47 (m,

br, 4H, H_p-BArf), 2.95 (s, 3H, Me_A), 2.91 (s, 3H, Me_B), 1.72 (m,

8.14 (AB system, J_HH) 8.8 Hz, 1H, H₅), 8.12 (AB system, J_HH

3

) 8.8 Hz, 1H, H₆), 7.80 (dd, ³J_PH) 11.5 Hz, ³J_HH) 8.2 Hz, ⁴J_HH

2

3

6H, P-CH₂CH₃), 0.87 (m, 9H, P-CH₂CH₃), 0.84 (s, J_PtH) 72.5

) 1.6 Hz, 6H, H_o,o′-P), 7.69 (dd, J_PtH) 17.0 Hz, J_HH) 5.5 Hz,

Hz, ³J_PH) 3.0 Hz, 3H, Pt-CH₃). ³¹P NMR (CDCl₃): δ 3.4 (¹J_PtP

1260 Inorganic Chemistry, Vol. 44, No. 5, 2005

)

⁴J_HH) 1.1 Hz, 1H, H₉), 7.59 (dd, J_HH) 5.5, 8.2 Hz, 1H, H₈),

3

2,9-Dimethyl-1,10-Phenanthroline in Platinum(II) Complexes

Table 5. Experimental Data for the X-ray Diffraction Study of Compounds: 8, 11, 14, and 15^a

8

11

14

15

formula

mol wt

data coll T, K

cryst syst

space group (no.)

a, Å

C₅₅H₃₈BF₂₄N₂PPt

1419.74

293(2)

C₅₆H₄₈BF₂₄N₂PPt

1441.83

153(2)

C₆₅H₅₇BF₂₄N₂PPt

1559.00

293(2)

orthorhombic

Aba2 (41)

39.568(2)

17.767(2)

19.237(4)

90

13524(3)

8

C₃₁H₂₆F₆N₂P₂Pt

797.59

183(2)

triclinic

monoclinic

P21/n (14)

14.197(1)

30.075(2)

20.940(2)

90

107.275(2)

90

8538(1)

12

Ph1 (2)

P1h (2)

12.785(1)

14.513(2)

16.986(2)

103.605(2)

105.925(3)

101.266(2)

2829.5(5)

2

13.941(5)

14.030(5)

17.490(6)

102.594(8)

109.181(9)

108.253(8)

2865(2)

2

b, Å

c, Å

R, deg

â, deg

γ, deg

V, Å³

Z

F

_(calcd), g cm^-3

1.666

26.26

1.671

25.94

1.531

22.05

1.861

51.08

µ, cm^-1

θ range, (deg)

2.45 < θ < 27.03

1.64 < θ < 26.01

1.22 < θ < 26.03

1.95 < θ < 26.00

no. data collected

no. independent data

no. obs reflns (n_o₂)

25322

28013

60775

80178

12412

13272

16808

10915

9862

8743

9591

13988

2

[|F_o| > 2.0σ(|F| )]

no. of params refined(n_v)

766

903

1135

869

abs structure (Flack’s) param

0.023(8)

0.0283

0.0275

0.0722

0.930

0.023(8)

0.0461

0.067

0.023(8)

0.0701

0.0465

0.0805

0.994

0.023(8)

0.0437

0.0277

0.0603

1.039

b

R_av

R (obs reflns)^b

wR2 (obs reflns)^b

GOF^b

0.1674

0.996

b

2

^aDiffractometer, Bruker SMART CCD; radiation, Mo KR (graphite monochrom, λ ) 0.71073 Å. R_av) ∑|F_o- F_{o av}|/∑_i|F_o|; R ) ∑(|F_o- (1/

,

k)F_c|)/∑|F_o|; wR2 ) [∑w(F_o- (1/k)F_c)²/∑w |F_o| ]^1/2; GOF ) [∑_w(F_o- (1/k)F_c)²/(n_o- n_v)]^1/2

.

2

2 2

2

7.56 (m, ³J_HH) 7.7 Hz, ⁴J_HH) 1.6 Hz, 3H, H_p-P), 7.49 (dd, ³J_HH

least squares⁵⁹(the function minimized being ∑[w(F_o²- (1/k)F_c²])²]).

To improve convergence, the C-F distances in the BArf moiety

at room temperature were constrained to be approximately equal.

For all structures, no extinction correction was deemed necessary.

The scattering factors used, corrected for the real and imaginary

parts of the anomalous dispersion, were taken from the literature.⁶⁰

The standard deviations on intensities were calculated in terms of

statistics alone. All calculations were carried out by using the PC

version of the programs WINGX,⁶¹SHELX-97,⁵⁹and ORTEP.⁶²

4

2

) 7.7, 8.2 Hz, J_PH) 2.2 Hz, 6H, H_m,m′-P), 0.92 (s, J_PtH) 69.8

3

Hz, J_PH) 3.3 Hz, 3H, Pt-CH₃). ³¹P{¹H} NMR (CDCl₃): δ 19.1

1

(s, J_PtP) 4395 Hz), -144.1 (¹J_FP) 714 Hz). Anal. Calcd for

C₃₁H₂₆F₆N₂P₂Pt: C, 46.68; H, 3.29; N, 3.51. Found: C, 46.77; H,

3.17; N, 3.57.

Variable-Temperature NMR Experiments. In a typical experi-

ment, approximately 20 mg of the complex was dissolved in the

appropriate volume of deuterated solvent (∼0.5 mL). The ¹H NMR

spectrum was recorded over a temperature range depending on the

rate of the fluxional motion (from 219 to 354 K for complexes

1-14 in CDCl₃). Either the aromatic H₄-H₇protons or the methyl

protons of the 2,9-disubstituted phenanthroline ligand were moni-

tored and used for the line-shape analysis of the spectra. The

exchange rates were calculated using the computer program gNMR

4.0.⁵⁶The activation parameters ∆H^qand ∆S^q, together with ∆G^q

(calculated at 340 K), were derived from a linear regression analysis

of Eyring plots.

Crystallography. Crystals of [Pt(Me)(Me₂-phen)(PMe₂(C₆H₅))]-

(BArf), 8, [Pt(Me)(Me₂-phen)(P(i-Pr)₃)](BArf), 11, [Pt(Me)(Me₂-

phen)(PCy₃)](BArf), 14, and of [Pt(Me)(phen)(P(C₆H₅)₃)](PF₆), 15,

suitable for X-ray diffraction, were obtained by crystallization from

dichloromethane-n-hexane solutions and are air stable. All crystals

were mounted on a Bruker SMART diffractometer, equipped with

a CCD detector, for the unit cell and space group determinations.

Crystals 11 and 15 were cooled, using a cold nitrogen stream, to

153(2) and 183(2) K, respectively, for the data collection, while

for 8 and 14 data were collected at room temperature.

Structural Study of [Pt(Me)(Me₂-phen)(PMe₂(C₆H₅))](BArf),

8. From the lattice symmetry, the space group was assumed to be

Ph1 and later confirmed by the successful refinement. The cell

constants were refined by least squares at the end of the data

collection using 965 reflections (θ_maxe 25.2°). The BArf anion

shows, as expected, large amplitude vibrational displacements and

disorder in four of the eight substituted phenyl rings that could be

modeled satisfactorily assuming two different orientations for the

CF₃groups, as obtained from difference Fourier maps. The two

orientations were refined using anisotropic displacement parameters

for the F atoms; the occupancy factors for the two different

orientations are approximately equal (in the range 0.47-0.65). All

other atoms were refined using anisotropic displacement parameters,

except for the hydrogens; their contribution (calculated positions,

C-H ) 0.95(Å), B(H) ) 1.3/1.5 × B(C_bonded)(Å²), 1.5 was used

for the CH₃groups) was included in the refinement using a riding

model. Upon convergence, no significant features were found in

the Fourier difference map.

Structural Study of [Pt(Me)(Me₂-phen)(P(i-Pr)₃)](BArf), 11.

The space group was assumed to be Ph1 and confirmed by the

Experimental parameters and selected crystallographic and other

relevant data are listed in Table 5 and in the Supporting Information

(as a CIF file). Data were corrected for Lorentz and polarization

factors with the data reduction software SAINT⁵⁷and empirically

for absorption using the SADABS program.⁵⁸The structures were

solved by Patterson and Fourier methods and refined by full matrix

(58) Sheldrick, G. M. SADABS, Program for Absorption Correction;

University of Go¨ttingen: Go¨ttingen, Germany, 1996.

(59) Sheldrick, G. M. SHELX-97, Structure Solution and Refinement

Package; Universita¨t Go¨ttingen: Go¨ttingen, Germany, 1997.

(60) International Tables for X-ray Crystallography; Wilson, A. J. C., Ed.;

Kluwer Academic Publisher: Dordrecht, The Netherlands, 1992; Vol.

C.

(56) gNMR, version 4.0; Cherwell Science: Oxford, 1997.

(57) BrukerAXS, SAINT, Integration Software; Bruker Analytical X-ray

Systems: Madison, WI, 1995.

(61) Farrugia, L. J. J. Appl. Crystallogr. 1999, 32, 837-838.

(62) Farrugia, L. J. J. Appl. Crystallogr. 1997, 30, 565.

Inorganic Chemistry, Vol. 44, No. 5, 2005 1261

Romeo et al.

successful refinement. The cell constants (at 153K) were refined

by least squares at the end of the data collection using 918

reflections (θ_maxe 21.2°). The apparent large values of the ADPs

for the CF₃groups and the C1L carbon atom show the presence of

disorder. However, the presence of split positions was not shown

in the difference Fourier maps. Therefore, the anisotropic model

was retained. Anisotropic displacement parameters were used for

all atoms except the hydrogens. The hydrogen atoms, in their

calculated positions (C-H ) 0.95(Å), B(H) ) 1.3/1.5 × B(C_bonded)-

(Å²), 1.5 was used for the CH₃groups), were included in the

refinement using a riding model. Upon convergence, the final

difference Fourier map showed no significant peaks.

Structural Study of [Pt(Me)(Me₂-phen)(PCy₃)](BArf) 14. The

Aba2 space group was assumed, being consistent with the systematic

absences; the choice was confirmed by the successful refinement.

The cell constants were refined by least squares at the end of the

data collection using 979 reflections (θ_maxe 19.9°). The BArf anion

shows disorder in two of the eight substituted phenyl rings that

could be modeled satisfactorily assuming, for the CF₃groups, two

different orientations (obtained from difference Fourier maps). The

two orientations were refined using anisotropic displacement

parameters for the disordered C atoms; with occupancy factors for

the two carbons of 0.64 and 0.60, respectively. All other atoms

were refined using anisotropic displacement parameters. The

contribution of the hydrogen atoms, in their calculated positions

(C-H ) 0.95(Å), B(H) ) 1.3/1.5 × B(C_bonded)(Å²)), was included

in the refinement using a riding model. Refining the Flack’s

parameter tested the handedness of structure (cf. Table 5).⁶³Upon

convergence, no significant features were found in the Fourier

difference map.

Structural Study of [Pt(Me)(phen)(P(C₆H₅)₃)](PF₆), 15. The

space group was unambiguously determined from the systematic

absences, while the cell constants (at 183 K) were refined by least

squares at the end of the data collection using 1012 reflections (θ_max

e 25.3°). For the refinement, anisotropic displacement parameters

were used for all “heavy” atoms, while the hydrogen atoms, in their

calculated positions (C-H ) 0.95(Å), B(H) ) 1.3/1.5 × B(C_bonded)-

(Å²)), were included in the refinement using a riding model. Upon

convergence, the final Fourier difference map showed no significant

peaks.

Acknowledgment. We are grateful to a reviewer for

suggestions and to the Ministero dell’ Universita` e della

Ricerca Scientifica e Tecnologica (MURST), PRIN 2002 and

PRA 2003, for funding this work.

Supporting Information Available: ORTEP figures of com-

pounds 8, 11, 14, and 15 showing the full numbering schemes and

a figure showing the dependence of the Pt-N2 separation from

the symmetric deformation coordinate (S4′′); tables giving the

temperature dependence of the rate constants (k_f/s^-1) and the

associated activation parameters (∆H^q, ∆S^q, and ∆G^q) (PDFs); full

crystallographic data are available as CIF file (CCDC nos. 255085-

255088). This material is available free of charge via the Internet

at http://pubs.acs.org.

IC0485920

(63) Flack, H. D. Acta Crystallogr. 1983, A 39, 876-881.

1262 Inorganic Chemistry, Vol. 44, No. 5, 2005

Article Doi

Structural properties and dissociative fluxional motion of 2,9-dimethyl-1,10-phenanthroline in platinum(II) complexes

DOI: 10.1021/ic0485920

Source and publish data:

Authors:

Article abstract of DOI:10.1021/ic0485920

Full text of DOI:10.1021/ic0485920

Products guided by the article

R&D Labs maybe for 849519-13-7

Relevant to this article

Hot Product