From a PGeP Pincer-Type Germylene to Metal Complexes Featuring Chelating (Ir) and Tripodal (Ir) PGeP Germyl and Bridging (Mn2) and Chelating (Ru) PGeP Germylene Ligands

Article abstract of DOI:10.1021/acs.organomet.8b00171

Different coordination modes of a PGeP chloridogermyl ligand (Ge,P-chelating and P,Ge,P-tripodal) and a PGeP germylene ligand (P,Ge,P-bridging and Ge,P-chelating) have been identified in coordination compounds resulting from reactions of the PGeP pincer-t

Full text of DOI:10.1021/acs.organomet.8b00171

Article
Cite This: Organometallics XXXX, XXX, XXX−XXX
From a PGeP Pincer-Type Germylene to Metal Complexes Featuring
Chelating (Ir) and Tripodal (Ir) PGeP Germyl and Bridging (Mn2) and
Chelating (Ru) PGeP Germylene Ligands
†
‡
Javier Brugos,† Javier A. Cabeza,*,† Pablo García-Alvarez, and Enrique Perez-Carreno
́
́
̃
†Centro de Innovacion
́ ́ ́
en Química Avanzada (ORFEO-CINQA), Departamento de Química Organica e Inorganica, Universidad de
Oviedo, 33071 Oviedo, Spain
‡Departamento de Química Física y Analítica, Universidad de Oviedo, 33071 Oviedo, Spain
S
* Supporting Information
ABSTRACT: Different coordination modes of a PGeP chloridogermyl ligand (Ge,P-
chelating and P,Ge,P-tripodal) and a PGeP germylene ligand (P,Ge,P-bridging and
Ge,P-chelating) have been identified in coordination compounds resulting from
reactions of the PGeP pincer-type diphosphane-germylene Ge(NCH2PtBu2)2C6H4 (1)
with iridium(I), manganese(0), and ruthenium(II) complex reagents. Germylene 1
reacted with [Ir2(μ-Cl)2(η4-cod)2] (cod = 1,5-cyclooctadiene) to give [Ir{κ2Ge,P-
GeCl(NCH2PtBu2)2C6H4}(η4-cod)] (2), which contains a Ge,P-chelating PGeP
chloridogermyl ligand and an uncoordinated phosphane group that weakly interacts
with the Ge atom. Carbon monoxide readily displaced the cod ligand of 2 to give the
dicarbonyl derivative [Ir{κ3P,Ge,P-GeCl(NCH2PtBu2)2C6H4}(CO)2] (3), in which the
PGeP chloridogermyl ligand displays a P,Ge,P-tripodal coordination mode. A bridging
germylene moiety has been identified in the binuclear derivative [Mn2{μ-κ3P,Ge,P-
Ge(NCH2PtBu2)2C6H4}(CO)8] (4), which resulted from the treatment of
[Mn2(CO)10] with germylene 1. The ruthenium complex [RuHCl(CO){κ2Ge,P-Ge(NCH2PtBu2)2C6H4}(PiPr3)] (5), which
was isolated from the reaction of 1 with [RuHCl(CO)(PiPr3)2], is the first transition-metal derivative of 1 in which the
germylene moiety has not inserted into an M−M or M−Cl bond (M = transition metal), as it contains germylene 1 coordinated
in a Ge,P-chelating mode, the resulting GeNCPRu ring being severely strained due to the short length of the coordinated
CH2PtBu2 arm, which also forces the germanium atom to be in an uncommon T-shaped environment. DFT calculations have
been used to shed light on bonding features of complexes 2 and 5. The X-ray structures of 1−5 are also reported.
equipped with at least one heavier tetrylene as a donor group:
Hahn and co-workers have described GeNGe and GeCGe
pincers in which a pyridine-2,6-diyl or a benzene-1,3-diyl group,
respectively, are linked to two 2-germabenzimidazol-2-ylidene
fragments,8 and also the NSnN pincers Sn{N-
(CH2)nNMe2}2C6H4 (n = 1, 2),9 but their behavior as ligands
has not been investigated; the Driess group has described the
synthesis, some coordination chemistry, and catalytic applica-
tions of ECE10 and ENE11 pincers having benzamidinato-
silylenes or -germylenes as E-donor groups; the groups of
Whited,12 Ozerov,13 and Zybill14 have reported some
transition-metal complexes containing the PSiP pincers Si-
(C6H4PPh2)2,12 Si(C6H4PiPr2)2,13 and Si(C6H4CH2PPh2)2,14
respectively, but their syntheses used silanes instead of free
silylenes; and we have recently communicated the synthesis and
INTRODUCTION
■
The use of heavier carbene analogues, also called heavier
tetrylenes, as ligands in transition-metal chemistry has increased
a great deal in the past few years.1 This intense research activity
has been stimulated by their ambiphilic character (they can
behave as Lewis bases and acids), by their strong electron-
donating capacity (those that are donor-stabilized are even
stronger electron donors than most phosphanes and N-
heterocyclic carbenes2), and by the discovery that some of
their complexes are efficient catalyst precursors for homoge-
neous catalytic transformations.3,4
On the other hand, many efforts have also been devoted in
the last two decades to the design and synthesis of pincer
ligands comprising strong electron-donating groups because
transition-metal complexes containing such ligands have been
successfully used in many stoichiometric5 and catalytic
reactions5,6 involving bond activation processes (strong
electron-donating ligands facilitate the participation of their
complexes in oxidative addition reactions7).
some transition-metal derivative chemistry of the metal-free
15,16
pincer-type PGeP germylene Ge(NCH2PtBu2)2C6H4
PSnP stannylene Sn(NCH2PtBu2)2C6H4.17
and
Despite the increasing interest in heavier tetrylenes and
pincer ligands, very few pincer-type ligands (free or forming
part of transition-metal complexes) have been reported to be
Received: March 22, 2018
© XXXX American Chemical Society
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Our aforementioned studies on the reactivity of germylene
Ge(NCH2PtBu2)2C6H4 (1) with transition-metal complexes
provided reaction products that resulted from the insertion of
the Ge atom of 1 into Co−Co15 or M−Cl (M = Rh,15 Ni,16
Pd,16 Pt16) bonds, but in no instance did we obtain a product
derived from the simple coordination (not insertion) of the
germylene fragment to a metal atom. We now report the
hitherto unknown X-ray diffraction (XRD) structure of
germylene 1 and reactions of this PGeP pincer-type germylene
with common iridium(I), manganese(0), and ruthenium(II)
complexes affording transition-metal derivatives in which we
have characterized chelating and tripodal PGeP germyl (Ir),
bridging PGeP germylene (Mn2), and unprecedented chelating
PGeP germylene (Ru) ligands, the last also representing the
first ruthenium complex to have a nondonor-stabilized N-
heterocyclic germylene coordinated as a terminal ligand.
RESULTS AND DISCUSSION
XRD Structure of Germylene 1. At the time we
communicated the synthesis of germylene 1 (Scheme 1),15 its
Figure 1. Two views of the XRD molecular structure of germylene 1
(35% displacement ellipsoids; H atoms omitted for clarity; atoms
marked with asterisks are related to unmarked atoms by a C2
symmetry axis). Selected interatomic distances (Å) and angles
(deg): Ge1···P1 3.320(2), Ge1−N1 1.879(4), P1−C4 1.890(5), P1−
C8 1.880(6), P1−C9 1.861(5), N1−C9 1.473(5), N1−C10 1.379(6),
C10−C10* 1.436(9); N1−Ge1−N1* 84.0(2).
■
Scheme 1. Synthesis of Germylene 1
Scheme 2. Synthesis of Complexes 2 and 3
molecular structure could not be unambiguously determined. It
was inferred from spectroscopic data and from DFT
calculations. A subsequent in-depth DFT study on PEP
tetrylenes of the type E(NCH2PtBu2)2C6H4 (E = C, Si, Ge,
Sn) concluded that the most stable conformation of the
molecules with E = Ge, Sn has the lone pairs of both P atoms
weakly interacting with empty orbitals with a large participation
of the Ge atom, resulting in unexpectedly short separations
between the E and P atoms, but this is not the case for the
lighter tetrylenes (E = C, Si).17
After many attempts, we have now been able to crystallize
germylene 1 and its molecular structure has finally been
determined by XRD. Figure 1 confirms that 1 has C2 symmetry
and that the P atoms, which are almost in the plane defined by
the atoms of the 2-germabenzimidazol-2-ylidene fragment, are
only 3.320(2) Å away from the Ge atom, a distance that is 0.6 Å
shorter than the sum of van der Waals radii of these elements.18
This structure is similar to that of the tin analogue
Sn(NCH2PtBu2)2C6H4, in which the Sn···P distances are
3.277(1) and 3.313(1) Å (in this case, the molecule is not
symmetric).17
Ir−Ge bond distance, 2.4275(3) Å, is comparable to those
measured in other iridium(I) complexes containing germyl
ligands.19 The insertion of nondonor-stabilized germylenes into
Ir−Cl bonds has seldom been observed.20 For comparison, it
should be noted that the metal atoms of the related known
PSiP silyl rhodium complexes [Rh{κ3P,Si,P-SiCl(C6H4PPh2)2}-
(η4-cod)] and [Rh{κ3P,Si,P-Si(OTf)(C6H4PPh2)2}(η4-nbd)]
(nbd = norbornadiene), which were respectively prepared
from the silane H2Si(C6H4PPh2)2 and [Rh2(μ-Cl)2(η4-cod)2]
or [Rh(η4-nbd)2]OTf, are pentacoordinated,21 probably
because the smaller size of their phosphane groups allows a
tridentate coordination of the corresponding PSiP silyl ligand in
the presence of the η4-diene ligand.
Iridium(I) Derivatives of Germylene 1. The iridium(I)
dimer [Ir2(μ-Cl)2(η4-cod)2] (cod = 1,5-cyclooctadiene) reacted
readily with germylene 1 (1:2 mole ratio) to give the
chloridogermyl complex [Ir{κ2Ge,P-GeCl(NCH2PtBu2)2C6H4}-
(η4-cod)] (2) as the only reaction product (Scheme 2).
An XRD study (Figure 2) confirmed the insertion of the Ge
atom into an Ir−Cl bond and that the resulting PGeP
chloridogermyl ligand is Ge,P-chelated to an Ir(η4-cod)
fragment. Therefore, the complex maintains an uncoordinated
phosphane fragment. This feature was also suggested by the
31P{1H} NMR spectrum of 2, which contains two uncoupled
resonances at 75.9 (coordinated P) and 29.7 (free P) ppm. The
A remarkable feature of the structure of complex 2 is that its
uncoordinated P atom is in the proximity of the Ge atom, at a
distance (3.361(2) Å) that is only 0.041 Å longer than that
found in free germylene 1. A similar structural feature has also
been observed in the related rhodium complex [Rh{κ2Ge,P-
GeCl(NCH2PtBu2)2C6H4}(η4-cod)], in which the separation
between the uncoordinated P atom and the Ge atom is
3.364(3) Å.15 Aiming at obtaining a rationale that could
account for these structural observations, we performed a DFT
study on complex 2. An analysis of the NBO second-order
perturbation donor−acceptor interactions revealed a non-
negligible interaction, 12.3 kcal mol−1, between the orbital
B
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of both phosphane fragments (as has been previously observed
in the PGeP pincer chloridogermyl square-planar metal
derivatives [Rh{κ3P,Ge,P-GeCl(NCH2PtBu2)2C6H4}(CO)]15
and [MCl{κ3P,Ge,P-GeCl(NCH2PtBu2)2C6H4}] (M = Ni, Pd,
Pt)).16 The XRD structure of complex 3 (Figure 4) confirmed
Figure 2. XRD molecular structure of complex 2 (35% displacement
ellipsoids; H atoms omitted for clarity; only one of the two positions
in which the methyl groups attached to C8 are disordered is shown).
Selected bond distances (Å) and angles (deg): Ir1−C25 2.199(3),
Ir1−C26 2.188(2), Ir1−C29 2.193(2), Ir1−C30 2.202(3), Ir1−P1
2.3652(6), Ir1−Ge1 2.4275(3), Ge1−N1 1.859(2), Ge1···P2 3.361(2),
Ge1−N2 1.866(2), Ge1−Cl1 2.2806(7), P1−C4 1.888(3), P1−C8
1.903(3), P1−C9 1.865(2), P2−C16 1.854(2), P2−C20 1.890(3),
P2−C24 1.890(3), N1−C9 1.430(3), N1−C10 1.374(3), N2−C15
1.399(3), N2−C16 1.451(3), C10−C15 1.421(4), C25−C26
1.395(4), C29−C30 1.402(4); P1−Ir1−Ge1 82.45(2), N1−Ge1−N2
85.78(9), N1−Ge1−Cl1 105.12(7), N2−Ge1−Cl1 99.15(7), N1−
Ge1−Ir1 106.00(7), N2−Ge1−Ir1 142.04(6), Cl1−Ge1−Ir1
111.68(2).
Figure 4. XRD molecular structure of complex 3 (30% displacement
ellipsoids; H atoms omitted for clarity). Only one of the two
analogous molecules found in the asymmetric unit is shown. Selected
bond lengths (Å) and angles (deg): Ir1−C101 1.897(5), Ir1−C102
1.903(5), Ir1−P1 2.388(1), Ir1−P2 2.407(1), Ir1−Ge1 2.3880(5),
Ge1−N1 1.865(4), Ge1−N2 1.856(4), Ge1−Cl1 2.203(1), P1−C4
1.889(6), P1−C8 1.899(6), P1−C9 1.880(5), P2−C16 1.899(5), P2−
C24 1.900(5), P2−C20 1.908(5), N1−C9 1.454(7), N1−C10
1.399(6), N2−C15 1.402(6), N2−C16 1.454(6), C10−C15
1.415(7); C101−Ir1−P1 96.4(2), C101−Ir1−P2 95.6(2), C101−
Ir1−Ge1 167.8(2), C101−Ir1−C102 97.2(2), C102−Ir1−P1
110.3(2), C102−Ir1−P2 112.3(2), C102−Ir1−Ge1 95.0(2), P1−
Ir1−P2 133.66(4), P1−Ir1−Ge1 79.41(3), P2−Ir1−Ge1 79.63(3),
N1−Ge1−N2 91.5(2), N1−Ge1−Cl1 107.5(1), N2−Ge1−Cl1
104.3(1), N1−Ge1−Ir1 112.0(1), N2−Ge1−Ir1 113.5(1), Cl1−
Ge1−Ir1 123.22(4).
that contains the lone pair of the uncoordinated P atom and the
LUMO of the molecule, which is mainly contributed by the Ge
atom and has a slight σ*(Ge−N) character (Figure 3).
the tridentate coordination of the PGeP chloridogermyl ligand
and the presence of two CO ligands on the iridium atom, which
is in a distorted-trigonal-bipyramidal ligand environment with
the Ge atom and a CO ligand in the axial positions. The
observed distortion is caused by the short length of the
CH2PtBu2 side arms, which does not allow the P atoms to reach
the ideal equatorial plane of the bipyramid and forces the N
atoms to be in a pyramidal environment (ideally, sp2-hybridized
N atoms are trigonal planar). In contrast to complex 2, in which
the larger cod ligand only allows a bidentate coordination of the
PGeP chloridogermyl ligand (see above), the smaller size of
carbon monoxide allows a tridentate attachment of the PGeP
chloridogermyl ligand in complex 3. Given the nonplanarity of
the GeP2Ir atom grouping in 3, the coordination type of its
PGeP ligand can be referred to as “tripodal” rather than
“pincer”. The stability of complex 3 toward CO loss confirms
the higher disposition of iridium(I), in comparison to
rhodium(I), to be pentacoordinate, since the reaction of the
rhodium cod complex [Rh{κ2Ge,P-GeCl(NCH2PtBu2)2C6H4}-
(η4-cod)] with CO gives a square-planar monocarbonyl PGeP
pincer derivative.15
Figure 3. Filled (left) and empty (right) orbitals of complex 2 involved
in the weak donor−acceptor interaction that accounts for the close
proximity of the uncoordinated phosphane group to the Ge atom
(NBO second-order perturbation donor−acceptor interaction anal-
ysis).
Analogous theoretical studies have shown that weak P···E (E
= Ge, Sn) donor−acceptor interactions are also responsible for
the most stable conformations of germylene 1, its tin analogue,
and also the ruthenium chloridostannyl complex [RuCl{κ2Sn,P-
SnCl(NCH2PtBu2)2C6H4}(η6-cym)] (cym = p-cymene).17
The dicarbonyl derivative [Ir{κ3 P,Ge,P-GeCl-
(NCH2PtBu2)2C6H4}(CO)2] (3) was quantitatively formed
when a solution of complex 2 in toluene was exposed to a CO
atmosphere (Scheme 2). Two strong νCO absorptions, at 2001
and 1956 cm−1, were observed in the IR spectrum of the
resulting solution; the low νCO values indicate that the metal
atom is electron rich (the two phosphane fragments and the
germyl ligand are strong electron donors). Its 1H, 13C{1H}, and
31P{1H} NMR spectra indicated mirror molecular symmetry
(Cs), with the 31P resonance appearing at a vey high chemical
shift, 116.3 ppm (in C6D6), suggesting a strained coordination
Reaction of Germylene 1 with [Mn2(CO)10]. The
binuclear manganese(I) complex [Mn2{μ-κ3P,Ge,P-Ge-
(NCH2PtBu2)2C6H4}(CO)8] (4) was obtained from a reaction
C
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in which a 1:1 mixture of [Mn2(CO)10] and germylene 1 was
heated in toluene at reflux temperature for 4 h (Scheme 3).
environment. Some germylene-bridged dimanganese complexes
are known, but they have not been prepared by germylene
insertion into Mn−Mn bonds.22 Although the insertion of
nondonor-stabilized germylenes into other metal−metal bonds
has been previously observed,15,23 the only hitherto reported
complex that is structurally related to compound 4 is the
dicobalt derivative [Co2{μ-κ3P,Ge,P-Ge(NCH2PtBu2)2C6H4}-
(CO)6], in which each Co atom is in a trigonal-bipyramidal
environment.15
Scheme 3. Synthesis of Complex 4
Reaction of Germylene 1 with [RuHCl(CO)(PiPr3)2]. The
coordinatively unsaturated ruthenium(II) complex [RuHCl-
(CO)(PiPr3)2], which has already shown a rich derivative
chemistry,24 reacted readily with germylene 1 to give
[RuHCl(CO){κ2Ge,P-Ge(NCH2PtBu2)2C6H4}(PiPr3)] (5)
and free tris(isopropyl)phosphane (Scheme 4). Its spectro-
Mixtures of products that slowly evolved toward complex 4
were observed at shorter reaction times when the reaction was
monitored by IR spectroscopy. After 4 h, the reaction mixture,
which contained no [Mn2(CO)10], did not change with time
and complex 4 was isolated in 56% yield after a chromato-
graphic separation. The mass spectrum of 4 displayed the
molecular ion, confirming its binuclear formulation. Its most
informative NMR spectrum was the 31P{1H}, which contained
only one (rather broad) resonance with a high chemical shift of
δ 142.7 ppm in CD2Cl2, indicating that both P atoms are
related by a symmetry element and that they are coordinated to
manganese (whose only natural isotope, 55Mn, has a nuclear
spin of I = 5/2 and a quadrupolar moment, provoking broad
NMR signals) in a strained arrangement (high chemical shift,
see above).
The XRD structure of complex 4 (Figure 5) confirmed the
insertion of the Ge atom of germylene 1 into the Mn−Mn
bond of the original dimanganese(0) reagent and that each
phosphane fragment is attached to a Mn(CO)4 unit, resulting
in a binuclear complex of approximate (noncrystallographic) C2
symmetry, with no metal−metal bond (the Mn···Mn distance is
4.5162(5) Å) and with both Mn atoms in an octahedral ligand
Scheme 4. Synthesis of Complex 5
scopic data indicated the absence of any symmetry, that the
complex maintains the original hydride (δH −8.73 ppm (dd, JHP
= 21.6 and 16.3 Hz)) and carbonyl (νCO 1916 (s) cm−1)
ligands, and that two of its three phosphane groups (δP 99.9
(d), 66.2 (d), 16.0 (s) ppm) are strongly coupled to each other
(JPP = 243.0 Hz), suggesting a mutually trans arrangement, but
they did not help to unambiguously establish its molecular
structure, which was determined by XRD (Figure 6).
Remarkably, in contrast with our initial expectation,
compound 5 does not contain a chloridogermyl moiety. In
fact, it is the first transition-metal derivative of compound 1 to
have the germylene moiety not inserted into M−M or M−X
(M = transition metal; X = halogen) bonds. Figure 6 shows that
compound 5 is a hexacoordinate ruthenium(II) complex in
which germylene 1 chelates the metal atom through the Ge
atom and the P atom of one of its phosphane groups. As
suggested by the 31P{1H} and 1H NMR spectra, the two
coordinated phosphane groups are trans to each other and cis
to the hydride ligand, which is trans to the germylene moiety.
The Ge,P-chelating attachment of ligand 1 to the Ru atom and
the short length of the CH2PtBu2 arms do not allow the
germylene fragment to coordinate in the expected symmetrical
manner, provoking the GeNCPRu ring to be severely strained.
Thus (a) although the Ru atom is in the plane of the 2-
germabenzimidazol-2-ylidene moiety, it is almost aligned with a
Ge−N bond (Ru1−Ge1−N2 166.5(2)°), with the Ge atom
being in an unusual (almost) T-shaped environment, (b) the
Ru1−P1 distance (2.413(2) Å) is notably longer than the
Ru1−P3 distance (2.386(2) Å), and (c) the Ru−Ge bond
length (2.434(1) Å), which cannot be compared with that of
any ruthenium complex having a terminal nondonor-stabilized
N-heterocyclic germylene ligand (such a complex has never
been reported), is also much longer than that of [RuCl-
{κ3P,Ge,P-GeCl(C6H4PPh2)2}(PPh3)] (2.3906(5) Å), which
contains a P,Ge,P-tripodal chloridogermyl ligand.25 The very
wide Ru1−Ge1−N2 angle of complex 5, 166.5(2)°, is
noteworthy because a search at the Cambridge Structural
Database has revealed that the widest angle hitherto reported
Figure 5. XRD molecular structure of complex 4 (35% displacement
ellipsoids; H atoms omitted for clarity). Selected interatomic distances
(Å) and angles (deg): Mn1···Mn2 4.5162(5), Mn1−Ge1 2.5127(5),
Mn1−P1 2.3801(8), Mn2−Ge1 2.5615(5), Mn2−P2 2.3817(8),
Ge1−N1 1.903(2), Ge1−N2 1.897(2), P1−C4 1.894(3), P1−C8
1.908(3), P1−C9 1.864(3), P2−C16 1.869(3), P2−C20 1.907(3),
P2−C24 1.907(3), N1−C9 1.445(4), N1−C10 1.403(4), N2−C15
1.393(4), N2−C16 1.449(4), C10−C15 1.418(4); N1−Ge1−N2
85.4(1), N1−Ge1−Mn1 97.48(7), N2−Ge1−Mn1 117.54(7), N1−
Ge1−Mn2 124.55(8), N2−Ge1−Mn2 99.99(7), Mn1−Ge1−Mn2
125.82(2).
D
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Figure 6. XRD molecular structure of complex 5 (35% displacement
ellipsoids; H atoms, except the hydride ligand, omitted for clarity).
Selected bond lengths (Å) and angles (deg): Ru1−C101 1.83(1),
Ru1−Cl1 2.498(3), Ru1−P1 2.413(2), Ru1−P3 2.386(2), Ru1−Ge1
2.434(1), Ge1−N1 1.838(8), Ge1−N2 1.838(7), P1−C4 1.912(9),
P1−C8 1.88(1), P1−C9 1.857(9), P2−C16 1.88(1), P2−C20 1.92(1),
P2−C24 1.89(1), P3−C27 1.86(1), P3−C30 1.87(1), P3−C33
1.85(1), N1−C9 1.45(1), N1−C10 1.38(1), N2−C15 1.41(1), N2−
C16 1.48(1), C10−C15 1.41(1); P1−Ru1−Ge1 81.06(6), P1−Ru1−
Cl1 86.01(8), P1−Ru1−C101 95.9(3), P1−Ru1−P3 168.85(9), P3−
Ru1−Ge1 108.11(7), P3−Ru1−Cl1 89.42(8), P3−Ru1−C101
89.0(3), Cl1−Ru1−Ge1 79.59(7), Cl1−Ru1−C101 177.3(3),
C101−Ru1−Ge1 98.8(3), N1−Ge1−N2 86.2(3), N1−Ge1−Ru1
106.1(2), N2−Ge1−Ru1 166.5(2).
Figure 7. Principal molecular orbital (HOMO-86) responsible for the
Ge−Ru bond of complex 5. Its composition is 69.32% Ge (81.45% s,
18.54% p, 0.01% d) and 30.68% Ru (18.00% s, 61.00% p, 21.00% d).
germylene moiety of into the Ru−Cl or Ru−H bond, we heated
at 100 °C a toluene solution of complex 5, but in all instances
(various reaction times) we got a mixture of products (31P
NMR analysis) that we could not separate or characterize.
CONCLUDING REMARKS
■
around a tricoordinate Ge atom is 159.8(1)°, found in
[WHCl{κ2Ge,P-Ge(CH2PMe2)Ar}(PMe3)3] (Ar = 2,6-
(trip)2C6H3); trip = 2,4,6-iPr3C6H2), which also features a
chelating germylene-phosphane ligand.26
An XRD study has established that the structure of the only
hitherto known pincer-type diphosphane-germylene Ge-
(NCH2PtBu2)2C6H4 (1) is that previously predicted by DFT
methods,15,17 which indicated that the most stable conforma-
tion of the molecule has the lone pairs of both P atoms weakly
interacting with empty orbitals mainly located on the Ge atom.
The isolation of compounds 2 and 4 has proven the
propensity of the Ge atom of 1 to end inserted into inorganic σ
bonds, such as Ir−Cl (2) and Mn−Mn (4). The
chloridogermyl (2) and germylene (4) moieties of these
reaction products are additionally attached to the metal atoms
through one (2) or two (4) of their phosphane groups. The
short distance found between the Ge atom and the pendant
phosphane group P atom of complex 2 has been rationalized by
DFT calculations. The synthesis of the trigonal-bipyramidal
dicarbonyl derivative 3 demonstrates that the PGeP chlor-
idogermyl ligand of complex 2 can also act as a P,Ge,P-tripodal
ligand.
As the asymmetric coordination of the germylene moiety of
complex 5 differs considerably from the symmetric coordina-
tion found for other nondonor-stabilized germylenes, such as
GeCl2,27 Ge{N(SiMe3)2}2,19,23,28 and some cyclic germy-
lenes,27,29 when they act as terminal ligands, we decided to
undertake a molecular orbital study to investigate the bonding
between the Ge and Ru atoms of complex 5. The principal
molecular orbital responsible for the Ge−Ru bond (NBO
analysis) is the HOMO-86 (Figure 7), which has σ character,
and its energy (−16.65 eV) is well below that of the HOMO
(−7.56 eV). The large contribution of the undirected (spherical
shape) Ge 4s atomic orbital to the HOMO-86 orbital of
compound 5 (the composition of this orbital is given in the
caption of Figure 7) implies that the overlap of the Ge lone pair
orbital with the appropriate metal orbital should be little
affected by the asymmetric disposition of the Ru atom with
respect to the germylene moiety. In fact, the very low energy of
the HOMO-86 orbital indicates that this overlap is quite
efficient. It is also notable that germylene 1 does not behave as
a π-acceptor ligand in complex 5, since no bonding molecular
orbitals displaying π-type overlaps between the Ge and Ru
atoms have been found. The long Ru−Ge bond length
(2.434(1) Å) should be a consequence of (a) the large
contribution of the Ge 4s atomic orbital to the Ru−Ge bond
(an hybrid sp2 orbital would lead to a more efficient σ overlap
than an s orbital) and (b) the absence of Ru to Ge π back-
bonding.
The reaction that led to complex 5, in which germylene 1 is
Ge,P-chelated to the ruthenium atom, is the first one to render
a transition-metal derivative that does not arise from an
insertion process but from a simple Ge,P-chelation of
germylene 1 to a metal atom. In complex 5, the short length
of its coordinated CH2PiPr2 arm provokes the Ge atom to be in
an uncommon T-shaped environment. A molecular orbital
analysis of complex 5 has shown that the germylene moiety
mainly uses its nondirectional Ge 4s orbital for the bonding
with the Ru atom.
This contribution, in conjunction with previous papers
dealing with the reactivity of the PGeP pincer-type germylene 1
with rhodium,15 cobalt,15 and group 10 metal complexes,16
helps demonstrate that transition-metal complexes containing
PGeP pincer germyl or germylene ligands can be prepared
Considering the possibility of inducing an intramolecular
rearrangement of complex 5 involving the insertion of the
E
DOI: 10.1021/acs.organomet.8b00171
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
[Mn2(CO)10] (31 mg, 0.08 mmol), and toluene (5 mL). The yellow
solution was stirred at reflux temperature for 4 h. The color changed
from yellow to red-brown. A flash chromatographic separation (2 × 5
cm silica gel column packed in hexane), with dichloromethane as
eluent, afforded compound 4 as a red solid (37 mg, 56%). Anal. Calcd
for C32H44GeMn2N2O8P2 (Mw = 829.15 Da): C, 46.35; H, 5.35; N,
3.38. Found: C, 46.44; H, 5.47; N, 3.36. (+)-ESI LRMS: m/z found
830; calculated for [M]+ 830.06. IR (toluene): νCO 2050 (m), 2021
directly from the PGeP germylene, also opening up the
possibility to explore in the near future the involvement of
these complexes in catalytic adventures.
EXPERIMENTAL SECTION
■
General Procedures. Solvents were dried over appropriate
desiccating reagents and were distilled under argon immediately
before use. All reactions were carried out under argon in a dry
glovebox or using either Schlenk or vacuum-line techniques. Published
procedures were followed to prepare germylene 1,15 [Ir2(μ-Cl)2(η4-
cod)2],30 and [RuHCl(CO)(PiPr3)2].31 All remaining reagents were
purchased from commercial sources. The reaction products were
vacuum-dried for several hours prior to being weighed and analyzed.
IR spectra were recorded with a PerkinElmer Paragon 1000
spectrophotometer, using solution cells equipped with CaF2 windows.
NMR spectra were run on Bruker DPX-300 and NAV-400
instruments, using as standards the residual protic solvent resonance
1
(s), 1970 (sh), 1964 (s), 1947 (m), 1931 (s) cm−1. H NMR (C6D6,
300.1 MHz, 293 K): δ 6.84 (m, 2 H, 2 CH, of C6H4), 6.69 (m, 2 H, 2
CH, of C6H4), 4.09 (dd, JHH = 14.1 Hz, JHP = 8.4 Hz, 2 H, 2 CH of
PCH2), 3.05 (dd, JHH = 14.1 Hz, JHP = 10.3 Hz, 2 H, 2 CH of PCH2),
1.16 (d, JHP = 12.3 Hz, 18 H, 6 CH3 of 2 tBu), 0.93 (d, JHP = 12.5 Hz,
18 H, 6 CH3 of 2 tBu) ppm. 13C{1H} NMR (CD2Cl2, 100.6 MHz, 293
K): δ 220.3-214.4 (m, COs), 146.7 (s, 2 C of C6H4), 116.5 (s, 2 CH of
C6H4), 109.6 (s, 2 CH of C6H4), 41.6 (s, br, 2 CH2 of 2 PCH2), 37.7
(s, br, 4 C of 4 tBu), 30.7 (s, 6 CH3 of 2 tBu), 30.3 (s, 6 CH3 of 2 tBu)
ppm. 31P{1H} NMR (CD2Cl2, 162.0 MHz, 293 K): δ 142.7 (s) ppm.
[RuHCl(CO){κ2Ge,P-Ge(NCH2PtBu2)2C6H4}(PiPr3)] (5). In a dry-
box, a vial was charged with germylene 1 (173 mg, 0.35 mmol),
[RuHCl(CO)(PiPr3)2] (170 mg, 0.35 mmol), and toluene (3 mL).
The yellow solution was stirred at room temperature for 1 h (no color
change was observed) and was evaporated to dryness. The residue was
washed with hexane (3 × 3 mL) and vacuum-dried to give 5 as a
yellow solid (209 mg, 73%). Anal. Calcd for C34H66ClGeN2OP3Ru
(Mw = 820.97 Da): C, 49.74; H, 8.10; N, 3.41. Found: C, 49.93; H,
8.22; N, 3.36. ESI LRMS: no useful spectrum could be obtained. IR
(toluene): νCO 1916 (s) cm−1. 1H NMR (C6D6, 400.1 MHz, 293 K): δ
7.54 (m, 1 H, 1 CH, of C6H4), 7.19−7.15 (m, 2 H, 2 CH, of C6H4,
overlapped with the solvent peak), 7.05 (m, 1 H, 1 CH of C6H4), 4.35
(d, JHP = 14.2 Hz, 1 H, 1 CH of PCH2), 4.17−3.93 (m, 3 H, 3 CH of 2
PCH2), 2.71 (m, 3 H, 3 CH of PiPr3), 1.56−1.36 (m, 30 H, 10 CH3 of
1
for H (δ(C6HD5) 7.16 ppm; δ(CHDCl2) 5.32 ppm), the solvent
resonance for 13C (δ(C6D6) 128.4 ppm; δ(CD2Cl2) 54.0 ppm), and
aqueous 85% H3PO4 as an external reference for 31P (δ(H3PO4) 0.0
ppm); 13C assignments were done with the help of DEPT-135 spectra.
Microanalyses were obtained with a PerkinElmer 2400 microanalyzer.
Mass spectra (LRMS) were obtained with a Bruker Impact II mass
spectrometer operating in the ESI-Q-ToF positive mode; data given
refer to the most probable isotopomer.
[Ir{κ2Ge,P-GeCl(NCH2PtBu2)2C6H4}(η4-cod)] (2). In a drybox,
toluene (3 mL) was placed in a vial charged with germylene 1 (58
mg, 0.12 mmol) and [Ir2(μ-Cl)2(η4-cod)2] (40 mg, 0.06 mmol). The
mixture was stirred at room temperature for 30 min. The initial orange
color changed rapidly to dark red. The solvents were removed under
reduced pressure, and the residue was washed with hexanes (5 mL)
and vacuum-dried to give 2 as a red solid (80 mg, 82%). Anal. Calcd
for C32H56ClGeIrN2P2 (Mw = 831.05 Da): C, 46.25; H, 6.79; N, 3.37.
Found: C, 46.66; H, 6.82; N, 3.25. (+)-ESI LRMS: m/z found 859;
t
PiPr3 and Bu), 1.18−1.09 (m, 24 H, 8 CH3 of PiPr3 and tBu), − 8.73
(dd, JHP = 21.6 and 16.3 Hz, 1 H, RuH) ppm. 13C{1H} NMR (C6D6,
100.6 MHz, 293 K): δ 142.0 (s, C of C6H4), 141.7 (d, JC−P = 10.9 Hz,
C of C6H4), 119.5 (s, CH of C6H4), 117.8 (s, CH of C6H4), 111.8 (d,
1
calcd for [M − Cl + 2 MeOH]+ 859.33. H NMR (CD2Cl2, 300.1
JCP = 7.5 Hz, CH of C6H4), 109.9 (s, CH of C6H4), 42.7 (d, JCP = 22.4
MHz, 293 K): δ 6.75−6.60 (m, 4 H, 4 CH of C6H4), 5.29 (m, br, 2 H,
2 CH of cod), 5.19 (s, br, 2 H, 2 CH of cod), 3.72 (m, 1 H, 1 CH of
PCH2), 3.59 (m, 1 H, 1 CH of PCH2), 3.29 (m, br, 1 CH of PCH2),
3.06 (m, 1 H, 1 CH of PCH2), 2.25−1.75 (m, br, 8 H of 4 CH2 of
t
Hz, CH2 of PCH2), 37.8 (d, JCP = 15.7 Hz, C of Bu), 37.4 (d, JCP
=
11.8 Hz, C of tBu), 33.4 (d, JCP = 23.8 Hz, CH2 of PCH2), 32.4 (d, JCP
= 10.1 Hz, C of tBu), 32.2 (d, JCP = 11.4 Hz, C of tBu), 31.5 (s, 3 CH3
of tBu), 31.0 (s, 3 CH3 of tBu), 30.2 (d, JCP = 12.9 Hz, 3 CH3 of PiPr3),
30.0 (d, JCP = 12.5 Hz, 3 CH3 of PiPr3), 24.3 (d, JCP = 20.2 Hz, 3 CH of
t
cod), 1.38 (d, JHP = 11.6 Hz, 9 H, 3 CH3 of Bu), 1.29 (d, JHP = 12.1
t
t
Hz, 9 H, 3 CH3 of Bu), 1.19 (d, JHP = 12.2 Hz, 9 H, 3 CH3 of Bu),
t
t
PiPr3), 20.4 (s, 3 CH3 of Bu), 20.0 (s, 3 CH3 of Bu) ppm. 31P{1H}
NMR (C6D6, 162.0 MHz, 293 K): δ 99.9 (d, JPP = 243.0 Hz), 66.2 (d,
JPP = 243.0 Hz), 16.0 (s) ppm.
1.13 (d, JHP = 10.7 Hz, 9 H, 3 CH3 of Bu), ppm. 13C{1H} NMR
t
(CD2Cl2, 100.6 MHz, 293 K): δ 143.9 (d, JCP = 1.4 Hz, C of C6H4),
140.4 (d, JCP = 1.1 Hz, C of C6H4), 117.5 (s, CH of C6H4), 116.8 (s,
CH of C6H4), 109.5 (s, CH of C6H4), 108.8 (s, CH of C6H4), 81.5 (m,
br, 4 CH of cod), 42.1 (d, JCP = 16.0 Hz, 1 C of tBu), 38.8 (s, br, CH2
of PCH2), 36.6 (d, JCP = 14.6 Hz, 1 C of tBu), 33.5 (d, JCP = 34.2 Hz,
CH2 of PCH2), 33.0−32.0 (m, 2 C of tBu + CH2 of PCH2 + 4 CH2 of
X-ray Diffraction Analyses. Crystals of 1, 2, 3·0.75C7H8, 4·C7H8,
and 5 were analyzed by X-ray diffraction. They all were obtained in the
drybox by slow evaporation of toluene solutions contained in open
vials. A selection of crystal, measurement, and refinement data is given
in Table S1. Diffraction data were collected on an Oxford Diffraction
Xcalibur Onyx Nova single-crystal diffractometer with Cu Kα
radiation. Empirical absorption corrections were applied using the
SCALE3 ABSPACK algorithm as implemented in CrysAlisPro RED.32
The structures were solved using SIR-97.33 Isotropic and full matrix
anisotropic least-squares refinements were carried out using
SHELXL.34 All non-H atoms were refined anisotropically. H atoms
were set in calculated positions and were refined riding on their parent
atoms. The position of the hydride ligand of 5 was calculated with
XHYDEX.35 The methyls of one tert-butyl group of 2 (C8 is its
quaternary carbon) were disordered over two positions with a 68:32
occupancy ratio, requiring restraints on the geometrical and thermal
parameters. The toluene solvent molecules found in the crystal of 3·
0.75C7H8 were disordered about centers of symmetry and required
restraints on their geometrical and thermal parameters. The WINGX
program system36 was used throughout the structure determinations.
The molecular plots were made with MERCURY.37 CCDC deposition
numbers: 1829992 (1), 1829993 (2), 1829994 (3·0.75C7H8), 1829995
(4·C7H8), and 1829996 (5).
t
cod), 30.8−29.5 (m, 12 CH3 of 4 Bu) ppm. 31P{1H} NMR (C6D6,
162.0 MHz, 293 K): δ 75.9 (s), 29.7 (s) ppm.
[Ir{κ3P,Ge,P-GeCl(NCH2PtBu2)2C6H4}(CO)2] (3). In a Schlenk
tube, carbon monoxide was bubbled for 10 min through a toluene
(4 mL) solution of complex 3 (42 mg, 0.05 mmol). The color changed
from dark orange to yellow. The resulting solution was evaporated to
dryness to give 3 as a yellow solid (38 mg, 98%). Anal. Calcd for
C26H44ClGeIrN2O2P2 (Mw = 778.88 Da): C, 40.09; H, 5.69; N, 3.60.
Found: C, 40.16; H, 5.77; N, 3.55. (+)-ESI LRMS: m/z found 751;
calcd for [M − CO + H]+ 751.15. IR (toluene): νCO 2001 (vs), 1956
(vs) cm−1. 1H NMR (C6D6, 400.1 MHz, 293 K): δ 6.92 (m, 2 H, 2 CH
of C6H4), 6.85 (m, 2 H, 2 CH of C6H4), 3.39 (m, 2 H, 2 CH of
PCH2), 2.95 (m, 2 H, 2 CH of PCH2), 1.21 (m, 18 H, 6 CH3 of 2 tBu),
t
0.79 (m, 18 H, 6 CH3 of 2 Bu) ppm. 13C{1H} NMR (C6D6, 100.6
MHz, 293 K): δ 187.1 (t, JCP = 9.1 Hz, CO), 178.6 (t, JCP = 32.2 Hz,
CO), 146.8 (s, 2 C of C6H4), 120.0 (s, 2 CH of C6H4), 115.9 (s, 2 CH
of C6H4), 49.0 (s, 2 CH2 of 2 PCH2), 38.7 (s, 2 C of 2 tBu), 36.8 (s, 2
t
t
t
C of 2 Bu), 30.4 (s, 6 CH3 of 2 Bu), 29.8 (s, 6 CH3 of 2 Bu) ppm.
31P{1H} NMR (C6D6, 162.0 MHz, 293 K): δ 116.3 (s) ppm.
[Mn2{μ-κ3P,Ge,P-Ge(NCH2PtBu2)2C6H4}(CO)8] (4). A Schlenk
tube was charged with germylene 1 (40 mg, 0.08 mmol),
Theoretical Calculations. DFT calculations were carried out
using the wB97XD functional,38 which includes the second generation
F
DOI: 10.1021/acs.organomet.8b00171
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
of Grimme’s dispersion interaction correction39 as well as long-range
interaction effects. This functional reproduces the local coordination
geometry of transition-metal compounds very well, and it also corrects
the systematic overestimation of nonbonded distances seen for all the
density functionals that do not include estimates of dispersion.40 The
Stuttgart−Dresden relativistic effective core potential and the
associated basis sets (SDD) were used for the Ir41 and Ru atoms.42
The basis set used for the remaining atoms was cc-pVDZ.43 The
stationary points were fully optimized in the gas phase and confirmed
as energy minima (all positive eigenvalues) by analytical calculation of
frequencies. The orbital analysis was carried out within the NBO
framework.44 All calculations were carried out with the Gaussian09
package.45 The atomic coordinates of all the DFT-optimized structures
are given in the Supporting Information.
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Atomic coordinates for the DFT-optimized structures
(XYZ)
Accession Codes
CCDC 1829992−1829996 contain the supplementary crystal-
lographic data for this paper. These data can be obtained free of
charge via www.ccdc.cam.ac.uk/data_request/cif, or by email-
ing data_request@ccdc.cam.ac.uk, or by contacting The
Cambridge Crystallographic Data Centre, 12 Union Road,
Cambridge CB2 1EZ, UK; fax: +44 1223 336033.
AUTHOR INFORMATION
Corresponding Author
*E-mail for J.A.C.: jac@uniovi.es.
■
́
Vondung, L.; Langer, R. Polyhedron 2018, 143, 28−42. (d) Fernandez-
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Alvarez, F. J.; Lalrempuia, R.; Oro, L. A. Coord. Chem. Rev. 2017, 350,
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Chemistry & Applications, van Koten, G., Gossage, R. A., Eds.;
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Goldman, A. S. Chem. Rev. 2011, 111, 1761−1779. (j) Selander, N.;
ORCID
Javier A. Cabeza: 0000-0001-8563-9193
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
́
Szabo, K. J. Chem. Rev. 2011, 111, 2048−2076. (k) The Chemistry of
This work has been supported by MINECO-FEDER
(CTQ2016-75218-P, MAT2016-78155-C2-1-R, RYC2012-
10491, and CTQ2016-81797-REDC) and Gobierno del
Principado de Asturias (GRUPIN14-009 and GRUPIN14-
060) research grants.
Pincer Compounds; Morales-Morales, D., Jensen, C., Eds.; Elsevier
Science: Amsterdam, 2007. (l) Yamashita, M. Bull. Chem. Soc. Jpn.
2016, 89, 269−281. (m) Turculet, L. In The Chemistry of Pincer
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DOI: 10.1021/acs.organomet.8b00171
Organometallics XXXX, XXX, XXX−XXX