Unprecedented η1-Pbasal coordination of P4X3 molecules (X = S, Se). An experimental and theoretical study of the apical vs basal complexation dichotomy

Article abstract of DOI:10.1021/ic010559f

Reaction of [(triphos)Re(CO)₂(OTf)] (1) [triphos = MeC(CH₂PPh₂)₃; OTf = OSO₂CF₃] with P₄S₃ and P₄Se₃ yields pairs of coordination isomers, namely, [(triphos)Re(CO)₂{η¹-P_apical -P₄X₃}]⁺ (X = S, 2; Se, 5) and [(triphos)Re(CO)₂{η¹-P_basal -P₄X₃}]⁺ (X = S, 3; Se, 6). The latter represent the first examples of the η¹-P_basal coordination achieved by the P₄X₃ molecular cage. Further reaction of 2/3 and 5/6 mixtures with 1 affords the dinuclear species [{(triphos)Re(CO)₂}₂{(μ,η^1:1 -P_apical,P_basal-P₄X₃} ]²⁺ (X = S, 4; Se, 7) in which the unprecedented M-η¹-P_basal/η¹ -P_apical-M′ bridging coordination of the P₄X₃ molecule is accomplished. A theoretical analysis of the bonding properties of the two coordination isomers is also presented. The directionality of apical vs basal phosphorus lone pairs is also discussed in terms of MO arguments.

Full text of DOI:10.1021/ic010559f

Inorg. Chem. 2002, 41, 659−668
Unprecedented η1-P
Coordination of P X Molecules (X ) S, Se). An
basal
4 3
Experimental and Theoretical Study of the Apical vs Basal
Complexation Dichotomy
,‡
Elisabetta Guidoboni,† Isaac de los Rios,‡ Andrea Ienco,‡ Lorenza Marvelli,† Carlo Mealli,*
,†
,‡
Antonio Romerosa,§ Roberto Rossi,* and Maurizio Peruzzini*
Laboratorio di Chimica Nucleare ed Inorganica, Dipartimento di Chimica, UniVersita` di Ferrara,
Via L. Borsari 46, 44100 Ferrara, Italy, ISSECC-CNR, V. Jacopo Nardi 39,
50132, Florence, Italy, and AÄ rea de Qu´ımica Inorga´nica, Facultad de Ciencias,
UniVersidad de Almer´ıa, Almer´ıa, Spain
Received May 25, 2001
Reaction of [(triphos)Re(CO)2(OTf)] (1) [triphos ) MeC(CH PPh2)3; OTf ) OSO CF ] with P S and P Se3 yields
2
2
3
4
3
4
pairs of coordination isomers, namely, [(triphos)Re(CO)2{η1-Papical-P X }]+ (X ) S, 2; Se, 5) and [(triphos)Re-
4
3
(CO)2{η1-Pbasal-P X }]+ (X ) S, 3; Se, 6). The latter represent the first examples of the η1-P
coordination
4
3
basal
achieved by the P X molecular cage. Further reaction of 2/3 and 5/6 mixtures with 1 affords the dinuclear species
4
3
[{(triphos)Re(CO)2}2{µ,η1:1-Papical,Pbasal-P X }]2+ (X ) S, 4; Se, 7) in which the unprecedented M−η1-Pbasal/η1-
4
3
P
apical−M′ bridging coordination of the P X molecule is accomplished. A theoretical analysis of the bonding properties
4 3
of the two coordination isomers is also presented. The directionality of apical vs basal phosphorus lone pairs is
also discussed in terms of MO arguments.
Introduction
The neutral mixed-cage molecules E4X3 (E ) P, As; X )
S, Se) exhibit a unique and fascinating structure formed by
a tetrahedral array of pnicogen atoms with a homocyclic-E3
unit connected via three bridging chalcogen atoms to a single
pnicogen atom in apical position (I).1 The behavior of these
molecules as ligands toward transition metal species has been
widely studied, and a variety of modular pathways approach-
ing the disruptive fragmentation of the heptatomic cages,
particularly P4S3 and As4S3, have been documented.2-5
The primary complexation of these molecules has also
been accomplished, but the known compounds in which an
intact, not activated, E4X3 molecule behaves as a two-electron
* Authors to whom correspondence should be addressed. E-mail:
peruz@fi.cnr.it (M.P.).
† Universita` di Ferrara.
‡ ISSECC-CNR.
§ Universidad de Almer´ıa.
(1) Riess, J. G. In Rings, Cluster, and Polymers; Cowley, A. H., Ed.;
ACS Symposium Series 232; American Chemical Society: Washing-
ton, DC, 1983; p 17.
(2) Di Vaira M.; Stoppioni P.; Peruzzini M. Comments Inorg. Chem. 1990,
11, 1.
(3) Di Vaira M.; Stoppioni P. Coord. Chem. ReV. 1992, 120, 259.
(4) Wachter, J. Angew. Chem., Int. Ed. 1998, 37, 751.
(5) Goh, L. Y. Coord. Chem. ReV. 1999, 185/186, 257.
ligand toward a transition metal fragment are still scarce.
Such a topology, which requires a Lewis acid metal center,
has been accomplished in octahedral complexes, e.g.,
[M(CO)5-x(η1-P4S3)1+x] [M ) Mo, W, x ) 0 (II);6 M ) Cr,
Mo, W, x ) 1 (III);7 M ) Cr, Mo, x ) 2 (IV)7] as well as
in tetrahedral ones, e.g., [(NP3)M(η1-P4X3)] (V) [NP3 )
10.1021/ic010559f CCC: $22.00 © 2002 American Chemical Society
Published on Web 01/22/2002
Inorganic Chemistry, Vol. 41, No. 4, 2002 659

Guidoboni et al.
N(CH2CH2PPh2)3; M ) Ni, Pd; X ) S, Se].8,9 In all of the
latter compounds, characterized by either X-ray diffraction
analysis6,8-10 or 31P NMR spectroscopy,7 the cage molecule
is bonded to the organometallic fragment through the lone
pair of the apical phosphorus atom (II-V). Also, 1:2
inclusion complexes [{P4X3}{Ni(TMTAA)}2] [TMTAA )
5,7,12,14-tetramethyldibenzo[b,i]-[1,4,8,11]tetrazacyclotet-
radecinenickel(II)] have been recently characterized by
crystallographic methods.11,12 In keeping with the observed
reactivity, the apical P-donor of the P4S3 molecule assimilates
to a tertiary phosphine whereas the basal P atoms behave
like the triangular cyclo-P3 unit of one P4 molecule.13 Also,
the chalcogen atoms could have coordination capabilities
toward thiophilic and selenophilic organometallic frag-
ments.14 Therefore, it is surprising that P4X3-transition metal
complexes featuring either metal-to-Pbasal (VI) or metal-to-
chalcogen coordination modes (VII) have not yet been
described.
dissociates triflate in the presence of a variety of two-
electron-donor ligands to yield the adducts [(triphos)Re(CO)2-
(L)]n+ [n ) 1, L ) H2,16 CO,16 CNR,15 HCCR,17 carbene,17,18
vinylidene,17,18 allenylidene,17,18 THF,20 CH3CHO,20 RSH,20
H2S,21 P4;22 n ) 0, L ) H,16 halide,15,16 pseudohalide,15
σ-organyl17-19]. Particularly interesting for the present study
is the reaction of 1 with white phosphorus, which yields the
stable η1-P4 complex [(triphos)Re(CO)2(η1-P4)](OTf) in
excellent yield.22 In view of the latter result, the reactivity
of 1 has been tested also toward the P4X3 cages (X ) S,
Se).
Synthesis and Characterization of the Coordination
Isomers of P4S3. At room temperature, 1 readily reacts in
CH2Cl2 with 1 molar equiv of P4S3, producing a pale yellow
solution. Upon concentration of the solution under vacuum,
a microcrystalline solid may be isolated in fairly good yield.
The elemental analysis of the reaction crude confirms the
formation of the expected 1:1 adduct between the [(triphos)-
Re(CO)2]+ synthon and the P4S3 molecule (Scheme 1).
31P{1H} NMR spectroscopy of the reaction product in CD2-
Cl2 indicates the presence of two species in the approximate
ratio 1:7. The latter are interpreted as a pair of coordination
isomers differing for the bonding mode of the P4S3 ligand,
namely, [(triphos)Re(CO)2{η1-Papical-P4S3}]+ (2) and [(tri-
phos)Re(CO)2{η1-Pbasal-P4S3}]+ (3) (Scheme 1). The relevant
NMR parameters are listed in Table 1 together with the
labeling scheme adopted to identify the different phosphorus
nuclei. A comparison of the NMR properties of the coordi-
nated and uncoordinated P4X3 cage molecules is provided
in Table 2 and highlights the similarities and the differences
in the two series of complexes.
In this paper we report on the synthesis and characteriza-
tion of some rhenium(I) derivatives of P4S3 and P4Se3 which
in solution exist as a mixture of Re-η1-Papical and Re-η1-
Pbasal coordination isomers. Remarkably, the latter coordina-
tion mode is unprecedented. Moreover, we provide the first
and clear-cut evidence of dinuclear compounds which
combine the M-η1-Pbasal and M′-η1-Papical coordination
modes. In the latter compounds, an intact P4X3 molecule is
sandwiched between two organometallic fragments.
The electronic nature of the two possible monometallic
isomers has been analyzed, and the most significant results
have been discussed.
The less abundant isomer displays an AM2X3Z splitting
pattern consistent with the formulation [(triphos)Re(CO)2-
{η1-Papical-P4S3}]+ (2) in which the cage, responsible for the
X3Z part of the spin system, is coordinated to the metal via
the apical phosphorus atom. This has usually been found
for the few known coordination compounds containing an
intact molecule of tetraphosphorus trisulfide as a ligand.6-9
Noticeably, the rhenium-bonded PZ atom falls at δ 91.52 as
a slightly broadened doublet of pseudosextuplets. The large
separation between the two components of the multiplet is
due to the strong coupling of PZ with the trans-disposed
triphos phosphorus atom, PA (2JAZ 147.5 Hz), while the
observed pseudosextuplet multiplicity arises from similar
values of the geminal couplings involving the cis-disposed
triphos PM atoms (2JMZ 25.5 Hz) and the three equivalent PX
Results and Discussion
The octahedral complex [(triphos)Re(CO)2(OTf)] (1)15
[triphos ) MeC(CH2PPh2)3; OTf ) OSO2CF3] readily
(6) Cordes, A. W.; Joyner, R. D.; Shores, R. D.; Dill, E. D. Inorg. Chem.
1974, 13, 132.
(7) Jefferson, R.; Klein, H. F.; Nixon, J. F. J. Chem. Soc., Chem. Commun.
1969, 536.
(8) Di Vaira, M.; Peruzzini, M.; Stoppioni, P. Inorg. Chem. 1983, 22,
2196.
(9) Di Vaira, M.; Peruzzini M.; Stoppioni, P. J. Organomet. Chem. 1983,
258, 373.
(10) The existence of [Cr(CO)5(η1-As4S3)] has also been briefly mentioned.
See footnote 92 in ref 4.
(16) Bianchini, C.; Marchi, A.; Marvelli, L.; Peruzzini, M.; Romerosa, A.;
Rossi, R.; Vacca, A. Organometallics 1995, 14, 3203.
(17) Bianchini, C.; Marchi, A.; Marvelli, L.; Peruzzini, M.; Romerosa, A.;
Rossi, R. Organometallics 1996, 15, 3804.
(18) Bianchini, C.; Mantovani, N.; Marchi, A.; Marvelli, L.; Masi, D.;
Peruzzini, M.; Rossi, R.; Romerosa, A. Organometallics 1999, 18,
4501.
(19) Bianchini, C.; Mantovani, N.; Marvelli, L.; Peruzzini, M.; Rossi, R.;
Romerosa, A. J. Organomet. Chem. 2001, 617/618, 233.
(20) Peruzzini, M.; Rossi, R. Unpublished results.
(21) Peruzzini, M.; de los Rios, I.; Romerosa, A. Prog. Inorg. Chem. 2001,
49, 169.
(22) Peruzzini, M.; Marvelli, L.; Romerosa, A.; Rossi, R.; Vizza, F.;
Zanobini, F. Eur. J. Inorg. Chem. 1999, 931.
(11) Andrews, P. C.; Atwood, J. L.; Barbour, L. J.; Nichols, P. J.; Raston,
C. L. Chem. Eur. J. 1998, 4, 1384.
(12) Andrews, P. C.; Atwood, J. L.; Barbour, L. J.; Croucher, P. D.; Nichols,
P. J.; Smith, N. O.; Skelton, B. W.; White, A. H.; Raston, C. L. J.
Chem. Soc., Dalton Trans. 1999, 2927.
(13) Head, J. D.; Mitchell, K. A. R.; Noodleman, L.; Paddock, N. L. Can.
J. Chem. 1977, 55, 669.
(14) Sulfur coordination of P4S3 has been postulated by Riess in the reaction
of the cage molecule with [M(CO)5(thf)] in THF on the basis of in
situ NMR analysis (see ref 1). However, in our hands, this result could
not be confirmed at least in the case of [Mo(CO)5(thf)].
(15) Bergamini, P.; Fabrizi De Biani, F.; Marvelli, L.; Mascellani, N.;
Peruzzini, M.; Rossi, R.; Zanello, P. New J. Chem. 1999, 207.
660 Inorganic Chemistry, Vol. 41, No. 4, 2002

η1-Pbasal Coordination of P4S3 and P4Se3 Molecules
Scheme 1
atoms of the P4S3 basal unit (2JXZ 23.4 Hz). An inset
expanding this multiplet is provided as trace a in Figure 1.
This is caused by a combination of strong one-bond coupling
to the metalated PQ (1JQX 235.8 Hz), sensible coupling to
the phosphorus sulfide PZ apex (2JXZ 70.3 Hz), and small
coupling to the apical triphos PA atom (3JXA 8.3 Hz). No
coupling to the two equatorial triphos PM atoms is recogniz-
able. Inset c in Figure 1 highlights the metalated PQ atom
which displays a remarkable 36 line multiplet easily com-
puted as a tddt pattern. This is due to large couplings to both
PX and the trans-disposed triphos PA atoms (2JQA 148.9 Hz)
and to minor couplings to PZ (2JQZ 41.6 Hz) and the two PM
atoms (2JQM 24.0 Hz). The apical PZ atom of the cage, no
longer coordinated to the metal, resonates at 85.20 ppm (trace
b in Figure 1) thus moving significantly downfield from the
In keeping with the proposed structure, the three basal PX
atoms give a broad doublet with only a discernible coupling
to the apical PZ phosphorus atom (trace d in Figure 1). The
triphos resonances, which for third-row transition metal
complexes15-19,22 fall slightly upfield with respect to the H3-
PO4 reference, exhibit multiplicities and coupling constants
consistent with the presence of the η1-Papical-P4S3 ligand. The
broadness of the resonances due to the phosphorus atoms of
the η1-Papical-P4S3 ligand is not easily explained. Remarkably,
the line widths of these signals do not change appreciably
on lowering the temperature of the CD2Cl2 solution down
to -60 °C.23 Accordingly, the only dynamic process must
be a fast rotation of the cage about its symmetry axis which
cannot be blocked even at the lowest accessible temperature.
free ligand value [∆ ) δ(PZ)3 - δ(P )
) 20.1 ppm]. The
Z P4S3
corresponding value for 2 is somewhat larger [∆ ) δ(PZ)2
- δ(P ) ) 26.4 ppm] as it could be expected in view of
Z P4S3
the coordination of PZ to the transition metal. Indirectly, the
comparison of the results for 3 and 2 suggests that coordina-
tion of PZ is not the only cause for the downfield chemical
shift. The triphos PA and PM atoms fall in the expected region
and exhibit dtt (PA) and dd (PM) multiplicities, respectively.
The major component of the reaction mixture exhibits an
AM2QX2Z spin system which agrees with the formation of
the coordination isomer [(triphos)Re(CO)2{η1-Pbasal-P4S3}]+
(3). Namely, the heptatomic cage is coordinated to rhenium
atom trough one basal phosphorus atom. The breaking of
the 3-fold symmetry in the P4S3 molecule determines the
most intriguing feature in the NMR spectrum of 3, i.e., the
appearance in the high-field part of the spectrum of two well-
separated resonances with an intensity ratio of 1:2. The less
intense signal, trace c in Figure 1, at δ -44.16, is assigned
to the unique phosphorus atom bonded to the metal (PQ)
while the other resonance at δ -134.17, trace e in Figure 1,
corresponds to the two nonmetalated basal phosphorus atoms
PX. The latter signal is moderately shielded with respect to
the three equivalent basal P atoms in 2 [∆ ) δ(Px)3 - δ(Px)2
) 15.6 ppm] as well as to free P4S324 [∆ ) δ(Px)3 - δ(Px)P S
Compounds 2 and 3 represent the first documented
example of coordination isomers of the P4S3 molecule and
are probably obtained through independent reaction pathways
which do not share any common intermediate. Remarkably,
the composition of the reaction mixture does not change on
varying the temperature from -60 to +50 °C (31P NMR
experiment in sealed NMR tube, CD2Cl2 solution), ruling
out the existence of any exchanging process between 2 and
3. Moreover, the final composition of the product mixture
from the reaction between 1 and P4S3 does not depend on
the temperature. In fact, the approximate product ratio 1:7
is unchanged when four samples of 1 and P4S3 thermostated
in CD2Cl2 were allowed to react completely at different
temperatures between -10 and +30 °C. At lower temper-
ature, no reaction occurs as the dissociation of the relatively
weak coordinated triflate ligand in 1 is prevented. Such an
experimental finding indicates that the two isomers are not
related to each other but are independently formed during
the reaction via two independent processes.
4
3
) 6.8 ppm] and is characterized by an eight-line multiplet.
(23) Below this temperature unspecific broadening of each resonance occurs
likely as a consequence of the increased solution viscosity and
magnetic field inhomogeneity.
(24) The 31P NMR spectrum of free P4S3 in CD2Cl2 at room temperature
consists of a ZX3 spin system with the following parameters: δ(PZ)
) 65.08, δ(PX) ) 127.33, (2JXZ 70.0 Hz). For comparison see also:
Di Vaira M.; Peruzzini M.; Stoppioni P. J. Chem. Soc., Dalton Trans.
1984, 359 and references therein.
Inorganic Chemistry, Vol. 41, No. 4, 2002 661

Guidoboni et al.
Table 1. 1H, 13C{1H}, and 31P{1H} NMR Spectral Data and IR Absorptions for the P4S3 and P4Se3 Rhenium(I) Complexese
662 Inorganic Chemistry, Vol. 41, No. 4, 2002

η1-Pbasal Coordination of P4S3 and P4Se3 Molecules
Table 1 (Continued)
a Confirmed by DEPT-135 experiment. b All 31P{1H} NMR were confirmed by 31P{1H}-COSY. Key: s, singlet; d, doublet; t, triplet; q, quartet; m,
multiplet; br, broad. c The 13C{1H} NMR resonances of 3 and 5 could not be safely assigned as both these complexes are formed in very minor concentration
and their resonances are likely masked by the most abundant species, and their IR bands could not be assigned for the same reason. d Due to the similarities
of JZM and JZX the multiplet appears as a doublet of pseudosextuplets, see text. e The NMR spectra were recorded in CD2Cl2 at room temperature using
Bruker AC200, Varian VXR300, and Bruker Avance DRX500 instruments.
Table 2. Comparison of the 31P{1H} NMR Data for the P4S3 and P4Se3 Ligands and the Rhenium(I) Complexes
chemical shift, ppm
Pbasal (PQ/X
J, Hz
compound
Papical (PZ)
)
JXZ
JQZ
JQX
P4S3
P4Se3
65.1
30.7
-127.3
-114.1
70
72
chemical shift, ppm
PX
J, Hz
compound
P
apical (PZ)
PQ
JXZ
JQZ
JQX
[(triphos)Re(CO)2{η1-Papical-P4S3}](OTf) (2-OTf)
[(triphos)Re(CO)2{η1-Pbasal-P4S3}](OTf) (3-OTf)
[{(triphos)Re(CO)2}2{µ,η1:1-Papical,Pbasal-P4S3}](OTf)2 (4-OTf)
91.52
85.20
93.10
-118.61
-134.17
-126.50
23.4
70.3
54.1
-44.16
-47.60
41.6
21.9
235.8
209.0
[(triphos)Re(CO)2{η1-Papical-P4Se3}](OTf) (5-OTf)
[(triphos)Re(CO)2{η1-Pbasal-P4Se3}](OTf) (6-OTf)
[{(triphos)Re(CO)2}2{µ,η1:1-Papical,Pbasal-P4Se3}](OTf)2 (7-OTf)
42.76
57.56
51.58
-108.74
-117.60
-110.78
28.1
69.5
45.2
-42.43
-42.48
48.8
15.6
238.2
210.0
very close to those reported for the [(triphos)Re(CO)2(η1-
P4)](OTf),22 suggesting similar electron donor capabilities
toward rhenium(I) for white phosphorus and tetraphosphorus
trisulfide.
Compounds 2-OTf and 3-OTf are air stable in the solid
state and, for a short exposure time, in solution of haloge-
nated solvents, THF, and acetone. They do not dissolve in
apolar solvents, diethyl ether, and alcohols. Column chro-
matography using CH2Cl2/n-hexane (3:1) as eluent enables
a separation of the major component 3 from 2. A pure sample
of compound 3-OTf can also be obtained by careful
crystallization from a dilute CH2Cl2/EtOH (5:1) solution.
Nevertheless, pure samples of 2-OTf could not be obtained
either through chromatographic methods or through fractional
crystallization. Solutions of 3 in CH2Cl2 under nitrogen are
quite stable and do not re-form 2 over weeks.
Figure 1. 31P{1H} NMR spectrum in CD2Cl2 of [(triphos)Re(CO)2{η1-
P
apical-P4S3}]+ (2) (*) and [(triphos)Re(CO)2{η1-Pbasal-P4S3}]+ (3) (O). The
symbol ∇ denotes a small amount of the dimer 4.
The IR spectrum (Nujol mull) is scarcely informative and
points out the presence of two broad and intense absorptions
due to the two equatorial carbonyl ligands of the [(triphos)-
Re(CO)2]+ moiety in complex 3. The absorptions of the
minor abundant isomer, 2, were not distinguished. As a
matter of fact, the two CO stretching absorptions of 3 fall
Synthesis and Characterization of the Dinuclear P4S3
Sandwich Complex [{(triphos)Re(CO)2}2{µ,η1:1-Papical,
-
Pbasal-P4S3}](OTf)2 (4-OTf). Depending on the stoichiometric
ratio between 1 and P4S3, the formation of the two isomers
2 and 3 may be accompanied by that of a third rhenium
Inorganic Chemistry, Vol. 41, No. 4, 2002 663

Guidoboni et al.
a in Figure 2). The latter has been computed as a dttd pattern
which arises from the coupling of PZ to PA, PX, and PC atoms,
with PA being the trans triphos atom (2JAZ 150.8 Hz), PX the
two equivalent, nonmetalated, basal atoms (2JXZ 54.1 Hz),
and PC the triphos P atoms lying trans to the CO ligands
(2JCZ 43.0 Hz). A final doubling of moderate magnitude with
the opposite metalated PQ nucleus halves each component
of the multiplet (2JQZ 21.9 Hz). The PQ resonance appears
as a tddt multiplet in which comparable values of the two
smaller coupling constants (2JQZ 21.9 Hz, 2JCQ 16.2 Hz) are
responsible for the gross appearance of this signal as a triplet
of broad quartets (see trace b in Figure 2). The triplet
multiplicity originates from large coupling to the two
uncoordinated PX atoms (1JXQ ) 209.0 Hz), which, in turn,
are responsible for the very high field shifted doublet of
doublets (δX -126.50) presented as trace c in Figure 2.
Although bimetallic [{Ir(CO)Cl(PPh3)(µ-P4S3)}2]25 or tri-
metallic [{Pt(PPh3)(µ-P4S3)}3]26 clusters containing two or
three bridging P4S3 molecules, respectively, resulting from
the P-P bond activation, are known, 4 is, to the best of our
knowledge, the first authenticated complex containing an
intact P4S3 molecule bridging two transition metal frag-
ments.27 The tetramer [(C5H5)4Cr4(CO)9(P4S3)],28 where the
skeleton of the original P4S3 cage is no longer evident due
to the numerous P-P and P-S bond cleavages, has also been
described.
Figure 2. 31P{1H} NMR spectrum in CD2Cl2 of [{(triphos)Re(CO)2}2-
{µ,η1:1-Papical,Pbasal-P4S3}]2+ (4) (O). The asterisk (*) denotes a small amount
of 3.
derivative, 4 (see Figure 1). The concentration of this latter
species increases when the reaction is carried out in less than
stoichiometric amount of P4S3, and 4 forms quantitatively
when 1 equiv of 1 is purposefully added to a solution of 2
and 3 (Scheme 1). A reasonable explanation is that the added
rhenium triflate complex reacts with each of the two
coordination isomers 2 or 3 forming the same binuclear
species of formula [{(triphos)Re(CO)2}2{µ,η1:1-Papical,Pbasal
-
P4S3}]2+ (4). The dimer 4 is therefore quantitatively produced
irrespective of the apical or basal coordination mode adopted
by the P4S3 ligand in the educt species and may be considered
as a sandwich complex in which a P4S3 molecule is tethering
two rhenium(I) fragments. Addition of 1/2 equiv of P4S3 to a
CH2Cl2 solution of 1 generates 4 in almost quantitative yield.
The two coordination isomers of P4S3 do not react with
additional 1 with the same speed notwithstanding they both
lead to 4. Thus, when a solution of 2 and 3 (1:7) is treated
with 0.2 equiv of 1 in CD2Cl2 at room temperature, the η1-
Papical-isomer, 2, disappears faster than 3 to yield 4. The
dimerization reaction is irreversible, and once formed the
dinuclear species 4 does not re-form 1 after prolonged staying
in dichloromethane solution. Conversely, addition of a 10-
fold excess of P4S3 to a solution of 4 in the same solvent
(NMR tube experiment) does not give back any of the two
monomers.
Synthesis and Characterization of Rhenium-P4Se3
Derivatives. The reaction of 1 with P4Se3 was accomplished
using the same protocol as for P4S3, the only significant
difference being due to the use of a CS2/CH2Cl2 mixture as
a solvent in order to increase the solubilty of the phosphorus
selenide. The results completely parallel those obtained for
P4S3, which is not surprising in view of the similar chemistry
of the two chalcogen derivatives.2-5,29 Thus, by treating 1
with P4Se3, a mixture of the two coordination isomers
[(triphos)Re(CO)2{η1-Papical-P4Se3}]+ (5) and [(triphos)Re-
(CO)2{η1-Pbasal-P4Se3}]+ (6) in approximately a 1:8 ratio is
formed. As found for the P4S3 system, the shortage of P4Se3
favors the formation of the dimeric species [{(triphos)Re-
(CO)2}2{µ,η1:1-Papical,Pbasal-P4S3}]2+ (7). The latter can be
In the 31P{1H} NMR spectrum of 4, the complicated
{AC2}{BD2}{QX2Z} spin system reflects the double meta-
lation of the P4S3 molecule {QX2Z spin system} which holds
together two nonequivalent triphos subunits [{AC2}{BD2}
spin system]. The absence of any discernible long-range
coupling between the two triphos subunits and the inspection
of the 31P{1H},31P{1H}-COSY 2D-NMR spectrum helped us
to unravel the 31P NMR spectrum shown in Figure 2. The
analysis of the network of correlation peaks involving the
two metalated PQ and PZ atoms as well as the triphos PA
and PB apical resonances in the COSY spectrum was
particularly useful to assign the two triphos subunits
which fall in a very narrow region between -9.5 and -12.8
ppm.
(25) Ghilardi, C. A.; Midollini, S.; Orlandini, A. Angew. Chem., Int. Ed.
Engl. 1983, 22, 790.
(26) Di Vaira M.; Peruzzini M.; Stoppioni P. J. Chem. Soc., Dalton Trans.
1985, 291.
(27) Although the present NMR analysis does not leave doubts to the
solution structure of complex 2-4, our several attempts to grow good
quality crystals suitable for an X-ray analysis were frustrated by
intrinsic difficulties because fibrous or twinned crystals were regularly
obtained. When transparent and well-formed crystals were apparently
grown (from diluted CH2Cl2/EtOH mixtures), a fast evaporation of
dichloromethane from the selected crystal hampered our attempts to
get a crystallographic analysis.
(28) Goh, L. Y.; Chen, W.; Wong, R. C. S.; Kararghiosoff, K. Organo-
metallics 1995, 14, 3886.
(29) Gysling H. J. In The Chemistry of Organic Selenium and Tellurium
Compounds; Patai, S., Rappaport, Z., Eds.; John Wiley: New York,
1986; Vol. 1., Chapter 18, pp 754-758.
The examination of the three multiplets due to the µ,η1:
1-Papical,Pbasal-P4S3 ligand reveals that the apical cage atom
PZ appears as a broadly resolved multiplet at δ ) 93.10 (trace
664 Inorganic Chemistry, Vol. 41, No. 4, 2002

η1-Pbasal Coordination of P4S3 and P4Se3 Molecules
prepared straightforwardly by reacting 1 with a half propor-
tion of P4Se3 or by treating a mixture of 5 and 6 with 1.
Complexes 5-7 share with the sulfido analogues most of
their chemical and physical properties. However, the three
selenido complexes are only moderately air stable and, within
1 h, decompose to an intractable tanned material in a solution
of dichloromethane, acetone, or THF unless a protective
nitrogen atmosphere is provided. The 31P NMR properties
of 5-7 are similar to those of 2-4 with the notable
difference due to the 77Se nucleus (77Se: I ) 1/2; 7.2% natural
abundance). The occurrence of the 77Se-isotopomer “77Se1-
P4Se3” causes each signal of P4Se3 to be flanked by broad
1
bumps due to the JPSe coupling.30 NMR features of 5-7
worth mentioning are (i) the almost identical values of the
metalated PQ atoms in both 6 and 7; (ii) the closeness of the
PX and PQ chemical shifts for 5-7 with those of the P4S3
analogues 2, 3, and 4; and (iii) the larger deviation of the
δPZ values on passing from the sulfido complexes 2-4 to
the selenido species 5-7. The latter finding reflects the large
difference of the PZ chemical shift for P4S3 in comparison
to P4Se3 [∆ ) δ(PZ)P S - δ(PZ)P Se ) 34.4 ppm] (Table 2).
4
3
4
3
The coordination chemistry of P4Se3 is still less studied
than that of P4S3, the only well-documented compounds
containing the intact P4Se3 molecule being the complexes
[(NP3)M(η1-P4Se3)] (M ) Ni, Pd).9 A more or less complete
fragmentation of the P4Se3 cage takes place in all the other
reactions combining this cage molecule and a transition metal
fragment.2-5,29 In the case of Goh’s tetramer [(C5H5)4-
Cr4(CO)9(P4Se3)],31 the original topology is no longer evident
as a result of multiple breakages of both P-P and P-Se
bonds.
Theoretical Calculations. In this section we will discuss
some aspects of the electronic structure of the isomers 2 and
3 and the directional features of the basal lone pairs at the
P4S3 cage. The simplified models 2m and 3m, which consist
of three individual PH3 molecules in place of the tripodal
ligand triphos, have been optimized using the DFT method.
Figure 3 reports the optimized structures of 2m and 3m
as well as that of the free P4S3 cage (C3V symmetry). Both
complexes have Cs symmetry with one P-S vector projecting
over the bisector of the P-Re-P equatorial angle. Since the
X-ray structures of two complexes 2 and 3 are not available,
the computed geometric details are particularly important in
this case. Thus, the bond distances are directly reported in
the drawings of 2m and 3m, and a selection of the angular
values is given in Table 3.
Figure 3. Optimized structures of model complexes 2m and 3m as well
as that of the free P4S3 cage. Distances are given in angstroms (Å); the
values in parentheses are the experimental ones from ref 32.
a
Table 3. Relevant Angles (deg) for 2m, 3m, and the Free Cage P4S3
2m (Cs)
3m (Cs)
free cage (C3V)
P1-S2-P3
P1-S4-P5
P5-P3-P7
S2-P1-S4
S4-P1-S6
S2-P3-P5
S4-P5-P3
Re-P1-S2
Re-P3-S2
Re-P3-P5
P8-Re-P9
P8-Re-P10
C-Re-C
101
101
60
101
101
103
104
116
100
103
61
103 (103)
103 (103)
60 (60)
99 (100)
99 (99)
99
100
106
102
104 (103)
104 (103)
118
128
91
91
91
91
90
91
a The values in parentheses refer to the experimental X-ray structure of
the cage molecule.32
Concerning the free cage, it may be seen that the calculated
P-P and P-S distances are systematically longer (by ca.
2%) than the experimental ones,32 given in parentheses. On
the other hand, the shape of the cage, when coordinated to
the metal, is barely affected in any case. Only a minor
compression is calculated for the apical bonding mode (the
P-S-P angles in 2m are ca. 2° smaller with respect to the
103° value of free P4S3). This is verified also from the
available crystal structures of η1-Papical metal complexes of
P4S3, e.g., [Mo(CO)5(η1-P4S3)]6 and [(NP3)Ni(η1-P4S3)]8
which confirm the close similarity of the free and coordinated
cages. In the unprecedented basal coordination, however, the
cage appears slightly asymmetric. For instance, the angle
P3-S2-P1 closes up to 100° whereas the other two P-S-P
(30) The widths of the multiplets of PZ and PQ in 6 as well as of PQ in 7
do not allow a correct estimation of the related 1J(P,Se) couplings.
However, the observation of two featureless bumps, representing the
external components of the 31P NMR resonance in those complexes
incorporating one 77Se-nucleus, close to the signal of PX in 6 and of
both PZ and PX in 7, suggests the occurrence of 1J(P,Se) values
comprised between 480 and 585 Hz. These values broadly match with
the wide unpredictability of 1J(P,Se), which is reported to vary between
200 and 1100 Hz; see: Verkade, J. G.; Quin, L. D. In Phosphorus-31
NMR Spectroscopy in Stereochemical Analysis; Verlag Chemie:
Weinheim, Germany, 1987; p 453. The solubility of the complexes
was not enough to allow us to run reliable 77Se NMR spectra.
(31) Goh, L. Y.; Chen, W.; Wong, R. C. S. Phosphorus, Sulfur Silicon
Relat. Elem. 1994, 93/94, 209. Goh, L. Y.; Chen, W.; Wong, R. C. S.
Organometallics 1999, 18, 306.
(32) Leung, Y. C.; van Houten, S.; Vos, A.; Wiegers, G. A.; Wiebenga, E.
H. Acta Crystallogr. 1958, 10, 574.
Inorganic Chemistry, Vol. 41, No. 4, 2002 665

Guidoboni et al.
angles remain as open as 103°. Also the P5-P7 bond,
opposite to the metal-coordinated P3 atom, is clearly more
elongated than its analogues (2.30 Å vs 2.26 Å).
The Re-P bond involving the cage is somewhat longer
in 3m than in 2m (2.44 Å vs 2.41 Å) thus suggesting a
stronger donor power of the apical P atom with respect to
the basal one. Whether coordinated or not, the Papical atom
of P4S3 does not change its pyramidality as the S-Papical-S
angle is equal to 100° in both 2m and 3m (and 99° in the
free cage). Finally, the Re-P-S angles are 116° in 2m while
the Re-P3-S2 one is 118° in 3m. The difference is minimum
although the latter angle is significantly related to the
direction of the lone pair donated to the metal (vide infra).
Also from the energetic point of view, the alternative
coordination modes of P4S3 are quite similar. As a matter of
fact, the isomer with the η1-Papical coordination is calculated
to be only 2.0 kcal mol-1 more stable than the η1-Pbasal one.
Single-point MP2 calculations, performed by using DFT
optimized geometries, double the ∆E value (4.0 kcal mol-1)
thus confirming the greater thermodynamic stability of 2m.
This is likely attributable to the shorter, hence stronger, Re-
Pcage coordination bond (2.41 vs 2.44 Å, in 2m and 3m,
respectively). In contrast, the experimental observation, that
complex 3 is experimentally 7 times more abundant than 2,
can be justified on the basis of pure statistics (3:1 the ratio
of existing basal vs apical P donors). After all, the difference
in thermodynamic stability of the two species is relatively
small and additional MP2 single-point calculations, which
include the effect of the dichloromethane solvent, reduce the
gap (∆E ) 2.1 kcal mol-1).
While the direction of the lone pair at the apical P atom
coincides with the 3-fold axis of the cage, it is interesting to
comment on the directionality of the basal lone pairs. By
adopting the natural hybrid orbital technique (NHO), as
implemented in the package Gaussian98,33 we calculated that,
for the free P4S3 cage, the direction of maximum electron
density pointing out from any basal P atom forms an angle
τ of 130° with the P3 plane. In 3m, the angle formed by
Re-P coordination bond is only slightly larger (133°).
Qualitative MO arguments are helpful in framing the nature
of the dative bond departing from one atom of the P3 ring
and its directionality.
Figure 4. Frontier MO region of the free P4S3 molecule.
tangential character with respect to the S3 triangle.34 Among
the remaining combinations (two of e type and three of a1
type), it is not straightforward to distinguish between three
sulfur and four phosphorus radial lone pairs as the MOs are
distributed quasi homogeneously over the seven atoms
(exceptionally, 3a1, receives minimum contribution from the
basal atoms). Thus, at least four MOs (the symmetric
components of the two e sets and those of the two lower a1
levels) are engaged in the bonding between one basal P atom
and the external σ acceptor.
The important lobes of the four P4S3 MOs involved in
donation are not equally oriented on the basal P3 plane (see
τ angles in Figure 4). Eventually, the direction of the donor-
acceptor bond is a resultant of four weighted components,
the prevailing one being 2es which, on account of its highest
energy, interacts most with the σ acceptor. Interestingly, the
corresponding τ angle of 130° matches the value of the NHO.
The two lower orbital components are more biased and
should contribute to reduce the angular value which is on
the contrary greater (133°). In actuality, the potential energy
curve for reorienting the (PH3)3(CO)2Re(I) fragment in the
τ range 125-140° is quite flat (∆E ) 1.4 kcal mol-1 at the
DFT level). Also, the P-Re overlap population is practically
unchanged. These results are quite intuitive for slightly
misaligning a σ orbital about an sp hybrid pointing in its
direction.35
Along the same lines, the somewhat wider range of the
angles between the P3 ring and one M-P bond departing
from it could be discussed for relatable systems. We refer
in particular to [(NP3)Ni(η1-P4)]36 [NP3 ) N(CH2CH2)-
PPh2)3], where the η1-coordinated P3 ring is part of a P4
molecule, or to [(triphos)Co{η3-P3(W(CO)5)2}],37 where the
same ring is capped by a metal fragment. In the two latter
species, the experimental τ angles are 161° and 143°,
respectively. A quantitative and qualitative MO analysis of
these compounds (to be reported elsewhere)38 suggests that
The frontier MO region of the free P4S3 molecule is
characterized by 10 filled levels, which identify with six
sulfur and four phosphorus lone pairs (see Figure 4).
The three highest 3e and a2 levels are uninvolved
combinations of the pπ orbitals of the sulfur atoms with
(33) Frisch, M. J.; Trucks, G. W.; Schlegel, H. B.; Scuseria, G. E.; Robb,
M. A.; Cheeseman, J. R.; Zakrzewski, V. G.; Montgomery, J. A.;
Stratmann, R. E.; Burant, J. C.; Dapprich, S.; Millam, J. M.; Daniels,
A. D.; Kudin, K. N.; Strain, M. C.; Farkas, O.; Tomasi, J.; Barone,
V.; Cossi, M.; Cammi, R.; Mennucci, B.; Pomelli, C.; Adamo, C.;
Clifford, S.; Ochterski, J.; Petersson, G. A.; Ayala, P. Y.; Cui, Q.;
Morokuma, K.; Malick, D. K.; Rabuck, A. D.; Raghavachari, K.;
Foresman, J. B.; Cioslowski, J.; Ortiz, J. V.; Stefanov, B. B.; Liu, G.;
Liashenko, A.; Piskorz, P.; Komaromi, I.; Gomperts, R.; Martin, R.
L.; Fox, D. J.; Keith, T.; Al-Laham, M. A.; Peng, C. Y.; Nanayakkara,
A.; Gonzalez, C.; Challacombe, M.; Gill, P. M. W.; Johnson, B. G.;
Chen, W.; Wong, M. W.; Andres, J. L.; Head-Gordon, M.; Replogle,
E. S.; Pople, J. A. Gaussian 98, revision A.9; Gaussian, Inc.:
Pittsburgh, PA, 1998.
(34) If we consider that each sulfur atom carries also an outpointing σ
lone pair, it may not be excluded that an appropriate transition metal
fragment which combines σ and dπ acceptor capabilities can achieve
the as yet unknown S-coordination of the cage. Possible candidates
to the purpose are d8-ML2 and d6-ML4 transition metal fragments.
(35) Gimarc, B. M. Molecular Structure and Bonding; Academic Press:
New York, 1979.
(36) Dapporto, P.; Midollini, S., Sacconi L. Angew. Chem., Int. Ed. Engl.
1979, 18, 469.
(37) Di Vaira, M.; Ehses, M. P.; Peruzzini, M.; Stoppioni, P. J. Organomet.
Chem. 2000, 593, 127.
(38) Mealli, C.; Ienco, A.; Peruzzini, M. Unpublished results.
666 Inorganic Chemistry, Vol. 41, No. 4, 2002

η1-Pbasal Coordination of P4S3 and P4Se3 Molecules
Synthesis of [{(triphos)Re(CO)2}2{µ,η1:1-Papical,Pbasal-P4S3}]-
(OTf)2 (4-OTf). Method A (from 1 and P4S3). A degassed solution
of 1 (0.50 g, 0.49 mmol) in dichloromethane (30 mL) was brought
to reflux, and 0.05 g of P4S3 (0.23 mmol) dissolved in 20 mL of
dichloromethane was added. The addition was completed in 20 min
while the solution was refluxed for 30 min under vigorous stirring.
Concentration of the solution to ca. 5 mL and addition of n-hexane
(10 mL) precipitated 4-OTf as a yellowish green microcrystalline
product. The compound was filtered under nitrogen and washed
with light-petroleum ether (2 × 5 mL) before being dried under
nitrogen. Yield: 0.42 g, 0.19 mmol (81%).
Method B (from 2/3 and 1). A solution of 2/3 (0.40 g, 0.33
mmol) in dichloromethane (25 mL) was treated with 1 equiv of
solid 1 (0.33 g, 0.32 mmol) and refluxed for 30 min. Workup as
above gave 4-OTf in ca. 75% yield (0.55 g, 0.24 mmol).
C88H78F6O10P10Re2S5: calcd C 46.93, H 3.49, S 7.12; found C 46.5,
H 3.7, S 7.3.
the Pbasal sp hybrids are significantly more bent with respect
to the P4S3 analogues. On the other hand, the donor power
of each P atom remains almost unchanged.
Concluding Remarks
This study provides sound experimental evidence that not
only the formation of the η1-Pbasal coordination of the P4S3
and P4Se3 cages is possible but, at least for the [(triphos)-
Re(CO)2]+ system under investigation, it exceeds the η1-
Papical isomer by a factor of 7 (8 for P4Se3). The DFT
calculations have permitted detailed description of the
structural features of the two isomers, which could not be
determined by X-ray diffraction in the lack of suitable
diffracting crystals. Moreover, the calculated energy differ-
ences between the coordination isomers are rather small, thus
suggesting that the prevalence of the basal coordination mode
may be simply attributable to statistics. The strength of the
basal vs apical lone pair does not seem to be a discriminating
factor also in view of the ease by which the contributing
donor orbitals can rehybridize, hence change direction.
Metathetical reaction of 4-OTf with NaBPh4 in CH2Cl2/EtOH
yielded the tetraphenylborate salt [{(triphos)Re(CO)2}2{µ,η1:1
-
Papical,Pbasal-P4S3}](BPh4)2 (4-BPh4). C134H118B2O4P10Re2S3: calcd
C 62.03, H 4.59, S 3.70; found C 61.6, H 4.6, S 3.4.
Reaction of [(triphos)Re(CO)2(OTf)] (1) with P4Se3. A solution
of 1 (0.50 g, 0.49 mmol) in dichloromethane (50 mL) was dropwise
added to a well-stirred solution of P4Se3 (0.18 g, 0.49 mmol) in
carbon disulfide (20 mL). The resulting yellowish red solution was
gently refluxed for 90 min before being concentrated to ca.10 mL
while hot. Cooling down to room temperature and addition of
n-hexane (10 mL) gave an orange solid, which was filtered under
nitrogen and washed with diethyl ether (2 × 5 mL) before being
dried under nitrogen. The NMR analysis indicates the formation
of a 1:8 mixture of the two coordination isomers 5 and 6. Yield:
0.57 g, 0.42 mmol (75%). FABMS: 867 (M+ - P4Se3); 839, 811
(M+ - P4Se3 - nCO, n ) 1-2). C44H39F3O5P7SSe3Re: calcd C
38.39, H 2.86, S 2.33; found C 38.8, H 3.0, S 2.0.
Experimental Section
General Information. Dichloromethane was purified by distil-
lation under nitrogen over P2O5. Carbon disulfide was reagent grade
and was used as received. Complex 1 was prepared as described
in the literature,15 and P4S3 was obtained from Fluka AG and was
recrystallized from benzene prior to use. P4Se3 was prepared from
red phosphorus and black selenium as described in the literature39
and purified by Soxhlet extraction with benzene. Deuterated
dichloromethane for NMR measurements (Aldrich) was dried over
1
molecular sieves (4 Å). H, 13C{1H}, and 31P{1H} NMR spectra
Synthesis of [{(triphos)Re(CO)2}2{µ,η1:1-Papical,Pbasal-P4Se3}]-
(OTf)2 (7-OTf). On replacing P4S3 with P4Se3 in the preparation
of 4-OTf, the corresponding dinuclear complex 7-OTf was obtained
as yellow microcrystals after similar workup. The use of a CH2-
Cl2/CS2 (1:1) solution was necessary in method A to efficiently
dissolve P4Se3. Yield: 76% (method A); 70% (method B).
C88H78F6O10P10Re2S2Se3: calcd C 44.17, H 3.29, S 2.68; found C
44.3, H 3.0, S 2.5.
Computational Details. The DFT calculations were performed
by using the Gaussian98 package.33 Structural optimizations were
carried out at the hybrid density functional theory (DFT) using the
Becke’s three-parameter hybrid exchange-correlation functional40
containing the nonlocal gradient correction of Lee, Yang, and Parr
(B3LYP).41 All optimized structures were confirmed as minima by
calculation of numerical vibrational frequencies. A collection of
Cartesian coordinates and total energies for all of the optimized
molecules are available from the authors upon request. The basis
set for the Rh atom utilized the effective core potentials of Hay
and Wadt42 with the associated double-ú valence basis functions.
The basis set used for the remaining atomic species was the 6-31G
one with the important addition of the polarization functions (d, p)
for all atoms, including hydrogens.
were recorded on Bruker AC200 or Bruker AVANCE DRX 500
spectrometers operating at 200.13 or 500.13 MHz (1H), 50.32 or
125.80 MHz (13C), and 81.01 or 202.45 MHz (31P), respectively.
Peak positions are relative to tetramethylsilane (1H and 13C) or H3-
PO4 85% with downfield values taken as positive (31P). The 31P,31P-
2D COSY NMR experiments were conducted on the AVANCE
DRX 500 Bruker spectrometer in the absolute magnitude mode
using a 90° pulse after the incremental delay. Infrared spectra were
recorded as Nujol mulls on a Perkin-Elmer 1600 series FT-IR
spectrometer between KBr plates. Mass spectra were recorded on
a Hewlett Packard MS Engine HP 5989A. Elemental analyses (C,
H, S) were performed using a Carlo Erba model 1106 elemental
analyzer.
Reaction of [(triphos)Re(CO)2(OTf)] (1) with P4S3. A dichlo-
romethane solution (30 mL) of 1 (0.50 g, 0.49 mmol) was treated
under nitrogen at room temperature with a solution of P4S3 (0.11
g, 0.49 mmol) in dichloromethane (20 mL) and stirred at room
temperature for 1 h. Concentration of the resulting yellow solution
under vacuum to ca. 15 mL and addition of n-hexane (20 mL) gave
pale yellow-colored microcrystals, which were filtered under
nitrogen and washed with light-petroleum ether (2 × 5 mL) before
being dried under a brisk current of nitrogen. The NMR analysis
indicates the formation of a 1:7 mixture of the two coordination
isomers 2 and 3. Yield: 0.52 g, 0.42 mmol (86%). FABMS: 867
(M+ - P4S3); 839, 811 (M+ - P4S3 - nCO, n ) 1-2).
C44H39F3O5P7ReS4: calcd C 42.76, H 3.18, S 10.37; found C 42.4,
H 3.3, S 10.5.
The starting geometry for optimization was derived from known
structures16-18 containing the [(triphos)Re(CO)2] fragment or the
(40) Becke, A. D. Phys. ReV. A 1988, 38, 3098.
(41) Lee, C.; Yang, W.; Parr, R. G. Phys. ReV. B 1998, 37, 785.
(42) (a) Dunning T. H.; Hay P. J. Modern Theoretical Chemistry, Schaefer,
H. F., III., Ed.; Plenum: New York, 1976; Vol. 3, p 1. (b) Hay, P. J.;
Wadt, W. R. J. Chem. Phys. 1985, 82, 299.
(39) Stoppioni P.; Peruzzini M. Gazz. Chim. Ital. 1988, 118, 581.
Inorganic Chemistry, Vol. 41, No. 4, 2002 667

Guidoboni et al.
uncoordinated cage P4S3.32 Frequency calculations ensured that the
obtained points were minima on the potential surfaces. The zero-
point energies for the two isomers are essentially equal (0.111
hartree) and were neglected for the comparisons of total energy.
Also, single-point MP2 ab initio calculations43 were performed at
the optimized geometries of the models 2m and 3m. The effect of
the chloroform solvent was calculated using the Isodensity PCM
model.44 The qualitative perturbation theory arguments used to
assess the lone pair directionality were developed through the usage
of the EHMO method45 and its graphics representations.46
tion of White Phosphorus”) and EC (INCO ERB-
IC15CT960746). I.d.l.R. thanks “Ministerio de Ciencia y
Tecnologia” (Spain) for a postdoctoral grant.
Note Added in Proof. While this paper was being
refereed, a comparable theoretical study of the alternative
bonding modes between the P4X3 unit (X ) S, Se) and σ
acceptor molecules such as BI3 and NbCl5 appeared in
Inorganic Chemistry.47 Some of these results were somewhat
earlier reported in the Journal of Molecular Modeling.48 In
agreement with our findings, the energy differences between
the apical and basal coordination modes are evaluated to be
very small (1-3 kcal mol-1).
Acknowledgment. This work was supported by INTAS
(Project 00-0018: “Towards an Ecoefficient Functionalisa-
(43) Møller, C.; Plesset, M. S. Phys. ReV. 1934, 46, 618.
(44) Foresman, J. B.; Keith, T. A.; Wiberg, K. B.; Snoonian, J.; Frisch,
M. J. J. Phys. Chem. 1996, 100, 16098.
(45) (a) Hoffmann, R.; Lipscomb, W. N. J. Chem. Phys. 1962, 36, 2872.
(b) Hoffmann, R.; Lipscomb, W. N. J. Chem. Phys. 1962, 37, 3489.
(46) (a) Mealli, C.; Proserpio, D. M. J. Chem. Educ. 1990, 67, 399. (b)
Mealli, C.; Ienco, A.; Proserpio, D. M. Book of Abstracts of the XXXIII
ICCC, Florence, 1998, 510.
IC010559F
(47) Aubauer, C.; Irran, E.; Klapo¨tke, T. M.; Schnick, W.; Schulz, A.;
Senker, J. Inorg. Chem. 2001, 40, 4956.
(48) Aubauer, C.; Klapo¨tke, T. M.; Schulz, A. J. Mol. Model. 2000, 6, 76.
668 Inorganic Chemistry, Vol. 41, No. 4, 2002