BCat ligand (Cat = catecholato). These results are in good
agreement with previous findings, which indicated a decrease
of the trans influence with increase of the electronegativity of
the boron-bound substituents.[22]
In summary, we have presented the first oxidative
addition of one boron–fluorine bond of BF3 to a transition
metal. As the product of the oxidative addition (4) is not
stable in solution, the fluoroboryl ligand could be preserved in
a subsequent reaction rendering the complex to the more
stable trans-chloro derivative 10; single-crystal X-ray diffrac-
tion was applied to both complexes. Furthermore, the
degradation product 3 could be obtained by an alternate
reaction pathway. All of the complexes were examined by
multinuclear NMR spectroscopy, both in the solid state and in
solution, and by IR spectroscopy, elemental analysis, and
DFT calculations.
Figure 1. Molecular structures of 4 and 10. Relevant bond lengths [ꢂ]
and angles [8]: 4: Pt–P1 2.325(1), Pt–P2 2.327(1), Pt–B1 1.965(3), Pt–
F3 2.272(2), B1–F1 1.327(4), B1–F2 1.336(3), B2–F3 1.441(3), B2–F4
1.379(4), B2–F5 1.369(4), B2–F6 1.375(4); P1-Pt-P2 170.1(1), P1-Pt-B1
90.6(1), P1-Pt-F3 90.0(1), F1-B1-F2 112.0(2), F3-B2-F4 107.0(2), F3-B2-
F5 107.0(4), F3-B2-F6 107.0(2), F4-B2-F5 111.8(2), F4-B2-F6 111.4(2),
F5-B2-F6 111.8(3). 10: Pt–P2.3187(6)); symmetry-related positions
(ꢀx, ꢀy, ꢀz) are labeled with ’. Ellipsoids set at 50% probability;
ellipsoids of the ligands, solvent molecules, and hydrogen atoms
omitted for clarity.
Experimental Section
General considerations regarding the experimental procedures, X-ray
diffraction, and computational studies are provided in the Supporting
Information.
4: In a Schlenk flask equipped with a Teflon valve, 1 (100 mg,
0.13 mmol) was dissolved in hexane (5 mL), cooled to ꢀ1968C, and
the flask was evacuated. At the same time, a gas trap with two Teflon
valves was filled with gaseous BF3 (18 mg, 0.26 mmol). After melting
of the reaction mixture, the BF3 was immediately added by
connection of the gas trap to the Schlenk flask (by opening the first
Teflon valve) and finally the vacuum was equalized with argon (by
opening the second valve of the gas trap). Under warming to room
temperature, the mixture was stirred for 15 min; meanwhile a
colorless precipitate was formed. After decanting off the solvent the
precipitate was washed two times with hexane, all volatiles were
removed in vacuo, yielding 102 mg of a colorless powder. The
constitution of the product was determined by solid-state NMR
spectroscopy as a 2:1 mixture of the product 4 and the degradation
product 3. Despite the instability in solution, a small amount of
crystals suitable for X-ray diffraction could be obtained instanta-
neously after addition of BF3 to a benzene solution of 1 in a Young
NMR tube. The crystals were found after 1 h at room temperature.
1H NMR (400.1 MHz, C6D6): d = 2.53ꢀ2.41 (m, 6H, Cy),
ꢀ
For example, the B1 F separations (1.327(4)/1.336(3) ꢁ) and
F1-B1-F2 angle (112.0(2)8) correspond with those (1.327(6)/
1.33(7) ꢁ; 110.8(5)8) reported for 2. The tetrafluoroborate
ligand reveals distortion from ideal tetrahedral geometry
ꢀ
owing to coordination to the Pt center. Thus, the B2 F3
separation of the bridging fluorine is increased (1.441(3) ꢁ)
compared to the mean separation of the terminal fluorine
substituents (1.374 ꢁ). Likewise, the F3-B2-F angles amount
to about 1078, whereas the other F-B2-F angles are about
1128. Overall, the BF4 ligand displays the typical structure for
h1-coordinated fluoroborates, as for example reported for
[(ItBu)(h3-C3H3)Pd(BF4)] (11).[21]
ꢀ
Recent work has shown that the length of the Pt Cl or the
Pt Br bond can be correlated with the degree of trans
ꢀ
influence exerted by boryl ligands in square-planar platinu-
m(II) complexes, but owing to disorder in the structure of 10,
this approach cannot be applied here.[12c,22] Therefore, density
functional calculations were carried out to compare the title
compounds with related complexes bearing different boryl
ligands. The optimized structures of the complexes
[(Cy3P)2Pt(X)(Br)] (X = BtBuBr (12), BCl2 (13), BBr2 (5),
BF2 (14), and Bcat (15)) were used to assess the relative trans
influence of the different boryl ligands (Table 2). According
to the calculated bond lengths, the fluoroboryl ligand reveals
a very weak trans influence, which is even smaller than that of
the bromoboryl ligand and only slightly larger than that of the
2.14ꢀ1.08 (m, 60H, Cy); 11B{1H} NMR (128.4 MHz, C6D6): d =
1
0.3 ppm; 13C{1H} NMR (100.6 MHz, C6D6): d = 35.4 (vt, N =j JP–C
+
2
3JP–C j= 27 Hz, C1 Cy), 30.6 (s, C3,5 Cy), 27.5 (vt, N =j JP–C + 4JP–C j=
11 Hz, C2,6 Cy), 26.8 ppm (s, C4 Cy); 19F{1H} NMR (376.5 MHz, C6D6):
d = ꢀ33.3 (vbr s, 2JPt–F = 1230 Hz), ꢀ167.0 ppm (vbr s); 31P{1H} NMR
(162.0 MHz, C6D6): d = 44.0 ppm (s, 1JPt–P = 2595 Hz); 31P HPDec/
MAS NMR (162.0 MHz): d = 42.0 ppm (s, 1JPt–P = 2550 Hz). IR: 1147,
1215 cmꢀ1 (BF2), 1115, 1174 cmꢀ1 (BF4). C,H analysis calcd. [%] for a
2:1 mixture of C36H66B2F6P2Pt and C36H67BF4P2Pt: C 49.38, H 7.64;
found: C 49.71, H 7.77.
3: In a Schlenk flask, 1 (100 mg, 0.13 mmol) was dissolved in 5 mL
(Et2O), and an excess of HBF4 (1 mL, 50% in Et2O) was added. After
stirring for 30 min, all volatiles were removed in vacuo, the residue
was extracted with toluene and again all volatiles were removed
in vacuo yielding 3 (93.4 mg, 0.11 mmol, 85%) as a colorless powder.
Table 2: Selected bond lengths [ꢂ] of DFT-optimized complexes.[a]
1H NMR (400.1 MHz, C6D6): d = 2.29ꢀ2.20 (m, 6H, Cy),
1
12
13
5
14
15
2.14ꢀ1.08 (m, 60H, Cy), ꢀ31.64 ppm (t, 2JP–H = 24 Hz, JPt–H
=
1806 Hz);
11B{1H} NMR
(128.4 MHz,
C6D6):
d = 0.2 ppm;
ꢀ
Pt Br
ꢀ
Pt B
2.739
2.013
2.698
1.987
2.695
1.980
2.692
2.002
2.689
2.013
1
13C{1H} NMR (100.6 MHz, C6D6): d = 34.8 (vt, N =j JP–C + 3JP–C j=
27 Hz, C1 Cy), 30.9 (s, C3,5 Cy), 27.5 (vt, N =j JP–C + 4JP–C j= 11 Hz,
2
[a] DFT methods using the 6-31G(d,p) basis set for H, B, C, Cl, F, O, P,
6-311G(d,p) for Br, and “Stuttgart Relativistic Small Core” ECP Basis Set
for Pt.
C2,6 Cy), 26.8 ppm (s, C4 Cy); 19F{1H} NMR (376.5 MHz, C6D6): d =
ꢀ169.0 ppm (vbr s); 31P{1H} NMR (162.0 MHz, C6D6): d = 48.1 ppm
(s, 1JPt–P = 2828 Hz); 31P HPDec/MAS NMR (162.0 MHz): d =
Angew. Chem. Int. Ed. 2011, 50, 10457 –10460
ꢀ 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim