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Scheme 3. Synthesis of trans-[Ir(4-C5NF4)(k2-(C,S)-SCS)(PiPr3)2] (3).
Figure 3. Computed structure for the transition state (TS2) of the
À
insertion of CS2 into the Ir F bond of 1a. The hydrogen atoms of the
isopropyl groups are omitted for clarity. Selected distances [ꢃ] and
angles [8]: Ir1–C1 2.016, Ir1–H1 1.556, Ir1–S1 2.609, Ir1–F5 2.197,
S1–C24 1.634, S2–C24 1.586, C24–F5 1.739; P1-Ir1-P2 165.5, C1-Ir1-H1
84.2, C1-Ir1-S1 108.6, C1-Ir1-F5 173.6, S1-C24-S2 148.8, S1-C24-F5
101.5, S1-C24-S2 109.7.
pointing towards the vacant trans position of the metal-bound
hydrogen atom of 1a (see the Supporting Information). As
the reaction proceeds, TS2 links to a shallow intermediate
(B1) at + 61.8 kJmolÀ1, and features a monodentate fluoro-
Figure 4. An ORTEP diagram of 3. Ellipsoids are drawn at the 50%
probability level. hydrogen atoms are omitted for clarity. Selected bond
length [ꢃ] and angles [8] with standard deviations in parentheses and
computed values in italics: Ir1–P1 2.391(3) 2.449, Ir1–P2 2.375(5)
2.446, Ir1–C1 2.038(9) 2.052, Ir1–C24 1.987(9) 1.973, Ir1–S1 2.459(2)
2.477, S1–C24 1.697(12) 1.685, S2–C24 1.602(11) 1.620; P1-Ir1-P2
166.58(9) 169.6, C1-Ir1-C24 124.4(4) 129.4, C1-Ir1-S1 169.3(3) 171.6,
Ir1-C24-S1 83.3(4) 84.8, Ir1-C24-S2 136.2(7) 134.3, S1-C24-S2 140.4(7)
140.8.
À
dithiocarbonato ligand. The C F separation of 1.388 ꢁ in B1
À
reveals the C F bond formation, whereas an Ir···F distance of
2.620 ꢁ denotes only a weak interaction between the metal
and the fluorine atom.[20] Subsequently, a rotation about the
À
C S bond and coordination of the second sulfur atom to Ir
results in the formation of 2a. Overall, the reaction path-
way B is computed to be kinetically favored over the
alternative route including HF elimination and CS2 coordi-
nation (pathway A). In addition, a mechanism which involves
a metallophosphorane intermediate generated by initial
migration of the fluorine atom to one of the phosphorous
atoms was computed to be unfavorable by an energy of
+ 272.6 kJmolÀ1.[8b,d,21]
Note that it was reported before that the reaction of 1a
with CO2 results in the formation of the hydrogencarbonato
complex trans-[Ir(4-C5NF4)(H)(k2-(O,O)-O2COH)(PiPr3)2]
(7) in the presence of traces of water.[13] An insertion of
features an almost square-planar arrangement of the phos-
phine ligands (P1-Ir1-P2 166.58(9) ꢁ), the apical carbon atom
of the tetrafluoropyridyl ligand and one sulfur atom of the CS2
ligand [C1-Ir1-S1 169.3(3)8]. The carbon atom of the CS2
ligand is bound to the metal with an C1-Ir1-C24 angle of
124.4(4)8. The C24-S1 bond [1.697(12) ꢁ] is found to be
longer than the C24-S2 bond [1.602(11) ꢁ], and the CS2
moiety is bent [S1-C24-S2 140.4(7)8] in a similar fashion as
reported for other compounds bearing a h2-CS2 ligand at
rhodium(I), nickel(0) or palladium(0).[23]
À
CO2 into the Ir F bond of 1a was not observed. We also
In accordance with the computational studies the iri-
dium(I) complex 3 does not react with Et3N·3HF (THF, 12 h,
508C, Scheme 3) or py·HF (C6D6, 12 h, 508C). Additionally,
the presence of CsF or Et3N·3HF does not have any influence
on the reaction rate for the conversion of 1a with CS2.
computed the formation of the putative insertion product
trans-[Ir(4-C5NF4)(H)(k2-(O,O)-O2COF)(PiPr3)2] by DFT
calculations and found it to be endothermic by
+ 32.9 kJmolÀ1. Furthermore, several attempts to optimize
a transition state comparable to TS2 only converged to the
structures of 1a and CO2.
À
However, the insertion of CS2 into the Ir F bond of 1a is
reversible at 508C. The complex 1a was observed by NMR
spectroscopy. The complex 3 was not detected, but several
other compounds were, and they could not be identified
further. To get more insight into that reaction, 2a was treated
with Ph3SnCl at 508C. This reaction led to the generation of
the chlorido complex trans-[Ir(4-C5NF4)(Cl)(H)(PiPr3)2]
(6)[13,24] and a colorless solid, which was identified as
Ph3SnF[25] by elemental analysis and IR spectroscopy
(Scheme 4). CS2 was detected in the reaction mixture by
GC/MS and 13C NMR experiments. We assume that initially
1a and CS2 are formed from 2a at elevated temperatures and
a subsequent reaction of 1a with Ph3SnCl yields the chlorido
Experimental studies gave further support for the improb-
ability of a fluorination of coordinated CS2. The complex
trans-[Ir(4-C5NF4)(h2-CS2)(PiPr3)2] (3) was prepared on treat-
ment of trans-[Ir(4-C5NF4)(h2-C2H4)(PiPr3)2] (5) with CS2
(Scheme 3). The 31P{1H} NMR spectrum of 3 shows a singlet
at d = 12.1 ppm for the phosphine ligands in a mutually trans
position. The 19F NMR spectrum of 3 displays four multiplets
at d = À98.4, À112.5, À118.0, and À117.2 ppm in a 1:1:1:1
ratio for the fluorine atoms of the tetrafluoropyridyl ligand.
The molecular structure of 3 was also confirmed by X-ray
diffraction analysis at À1738C (Figure 4).[22] The complex 3
ꢀ 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Angew. Chem. Int. Ed. 2013, 52, 11096 –11101