Three Fold Intramolecular Ring Closing Alkene Metatheses of Square

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Three Fold Intramolecular Ring Closing Alkene Metatheses of Square Planar Complexes with cis Phosphorus Donor Ligands P(X(CH) CH=CH) (X/m = –/5-10, O/3-5); Syntheses, Structures, and Thermal Properties of Macrocyclic Dibridgehead Diphosphorus Complexes 2

m

2

3

Hemant Joshi, Sugam Kharel, Andreas Ehnbom, Katrin Skopek, Gisela D. Hess, Tobias Fiedler, Frank Hampel, Nattamai Bhuvanesh, and John A. Gladysz J. Am. Chem. Soc., Just Accepted Manuscript • DOI: 10.1021/jacs.8b02846 • Publication Date (Web): 30 Apr 2018 Downloaded from http://pubs.acs.org on April 30, 2018

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Journal of the American Chemical Society

!!** REVISED **!! Three Fold Intramolecular Ring Closing Alkene Metatheses of Square Planar Complexes with cis Phosphorus Donor Ligands P(X(CH2)mCH=CH2)3 (X/m = –/5-10, O/3-5); Syntheses, Structures, and Thermal Properties of Macrocyclic Dibridgehead Diphosphorus Complexes Hemant Joshi,a‡ Sugam Kharel,a‡ Andreas Ehnbom,a Katrin Skopek,b Gisela D. Hess,b Tobias Fiedler,a Frank Hampel,b Nattamai Bhuvanesh,a and John A. Gladysz*a,b aDepartment

of Chemistry, Texas A&M University, PO Box 30012, College Station, Texas 77842-3012, USA. E-mail: [email protected]

bInstitut

für Organische Chemie and Interdisciplinary Center for Molecular Materials, Friedrich-

Alexander-Universität Erlangen-Nürnberg, Henkestraße 42, 91054 Erlangen, Germany. ABSTRACT: Reactions of cis-PtCl2(P((CH2)mCH=CH2)3)2 and Grubbs' first generation catalyst and then hydrogenations afford cis-PtCl2(P((CH2)n)3P) (cis-2; n = 2m+2 = b/12, c/14, d/16, e/18, f/20, g/22; 6-40%), derived from three fold interligand metatheses. The phosphite complexes cis-PtCl2(P(O(CH2)m*CH=CH2)3)2 are similarly converted to cis-PtCl2(P(O(CH2)n*O)3P) (cis-5; n* = a/8, b/10, c/12, 10-20%). The substitution products cis-PtPh2(P((CH2)n)3P) (cis-6c, d) and cis-PtI2(P(O(CH2)10O)3P) are prepared using Ph2Zn and NaI, respectively. Crystal structures of cis-2c,d,f, cis-5a,b, and cis-6c show one methylene bridge that roughly lies in the platinum coordination plane, and two that are perpendicular. The thermal behavior of the complexes is examined. When the bridges are sufficiently long, they rapidly exchange via an unusual "triple jump rope" motion over the PtX2 moieties. NMR data establish ∆H‡, ∆S‡, and ∆G‡298K/∆G‡ ‡ 393K values of 7.8 kcal/mol, –27.9 eu, and 16.1/18.8 kcal/mol for cis-2d, and a ∆G 393K of >19.6 kcal/mol for the shorter bridged cis-2c. While cis-2c,g gradually convert to trans-2c,g at 150-185 °C in haloarenes, trans-2c,g give little reaction under analogous conditions, establishing the stability order trans > cis. Similar metathesis/hydrogenation sequences with octahedral complexes containing two cis phosphine ligands, fac-ReX(CO)3(P((CH2)6CH=CH2)3)2 (X = Cl, Br), give fac-ReX(CO)3(P(CH2)13CH2)((CH2)14)(P(CH2)13CH2) (19-50%), which are derived from a combination of interligand and intraligand metathesis. The relative stabilities of cis/trans and other types of isomers are probed by combinations of molecular dynamics and DFT calculations. key words: alkene metathesis, platinum, rhenium, diphosphorus ligands, rotational barriers, jump rope processes, thermal isomerization, crystallography, DFT calculations submitted to J. Am. Chem. Soc.

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5 INTRODUCTION Multifold ring closing alkene (C=C) metatheses can lead to a variety of fascinating molecular architectures, especially in metal coordination spheres.1,2 Over the last fifteen years, we have been especially concerned with metathesis/hydrogenation sequences of the type exemplified in Scheme 1.3-7 These feature educts with trans disposed olefinic phosphine ligands of the formula P((CH2)mCH=CH2)3, such as the platinum dichloride complexes trans-1c-e (indices code to the number of atoms between phosphorus and the vinyl group). The major products are almost always derived from three fold interligand metatheses, which afford triply trans spanning dibridgehead diphosphine ligands. For trans-1c-e, this corresponds to trans-2c-e. In some cases, byproducts derived from combinations of interligand and intraligand metatheses are obtained, such as trans-2'c-e in Scheme 1. Such species carry primed numbers throughout this manuscript. Setaka has realized similar chemistry when the P-M-P linkages are replaced by Si-arylene-Si linkages (e.g., arylene = p-C6H4).2d,8 n-13

P((CH2)mCH=CH2)3 Cl Pt Cl

1. Grubbs' first generation catalyst, (Cy3P)2RuCl2(=CHPh)

P((CH2)mCH=CH2)3 m = 6, trans-1c 7, trans-1d 8, trans-1e P((CH2)mCH=CH2)3

2. H2/catalyst

P

n-13

Cl Pt Cl P

n = 2m+2

m = 6 (c), 8 (d), similar chemistry;

Cl Pd Cl P((CH2)mCH=CH2)3 m = 4 (a), 5 (b), oligomers/polymers

P

n-13

n-13

+

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

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Cl Pt Cl P

n-13

n = 14, trans-2c 16, trans-2d 18, trans-2e

trans-2'c trans-2'd trans-2'e

n-13

trans-2c / 2'c 43% / – (32% / 5%)a trans-2d / 2'd 04%b / 04%b trans-2e / 2'e 28% / 23% a larger scale reaction b yields from different experiments

Scheme 1. Three fold ring closing metatheses of trans-1c-e; syntheses of gyroscope like complexes trans-2c-e.4

Analogous reactions of palladium complexes with shorter methylene chains have been investigated, but only oligomeric or polymeric products were detected.4b,9 In any event, the monoplatinum complexes trans-2c-e represent an interesting class of molecular rotors.10 In all cases, rotation of the PtCl2 moieties about the P-Pt-P axes is rapid on the NMR time scale, even at –80 °C.4,11 Given the suggestive geometry, and the potential for closely related systems to function

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as molecular gyroscopes,8,10,12,13 we refer to them as gyroscope like. During the course of the efforts in Scheme 1, syntheses of the isomeric educts cis-1 were developed.14 Hence, it became of interest to investigate analogous metathesis/hydrogenation sequences, as sketched in Scheme 2. In the case of three fold interligand metathesis to give cis-2, a likely spatial distribution of macrocycles suggests (when the perpendicular Pt-Cl bonds are both directed downwards) a parachute (see I in Figure 1). Thus, we refer to cis-2 as parachute like. n-13

Cl

P((CH2)mCH=CH2)3 Pt P((CH2)mCH=CH2)3

Cl

1. Grubbs' first generation catalyst 2. 5 bar H2, 50-70 °C, cat. PtO2 or (Ph3P)3RhCl

n-13 n-13

P

Cl Pt Cl

P

n-13

P

Cl +

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Pt Cl

n-13

P

n-13

m = 5, 6, 7, 8, 9, 10,

cis-1b cis-1c cis-1d cis-1e cis-1f cis-1g

n = 2m+2

n = 12, cis-2b, 06% 14, cis-2c, 40% 16, cis-2d, 17% 18, cis-2e, 09% 20, cis-2f, 18% 22, cis-2g, 21%

cis-2'b cis-2'c cis-2'd cis-2'e cis-2'f cis-2'g

98%). See also Gabbaï, F. P.; Chirik, P. J.; Fogg, D. E.; Meyer, K.; Mindiola, D. J.; Schafer, L. L.; You, S.-L. An Editorial About Elemental Analysis. Organometallics 2016, 35, 3255-3256. (39) The PCH2CH2CH2 1H and 13C NMR signals of cis-1g and cis-2d,g were assigned by 1H,1H COSY, 1H,13C{1H} COSY, 13C{13C} COSY, and 1H,13C{1H} HMBC experiments. Representative spectra have been given for related compounds in earlier papers.6c,40 The corresponding signals of cis-1f and cis-2b,c,e,f were assigned analogously. (40) Lang, G. M.; Skaper, D.; Shima, T.; Otto, M.; Wang, L.; Gladysz, J. A. Syntheses of Iron(0) Complexes of Symmetrical Trialkylphosphines with Three Terminal Vinyl Groups, P((CH2)mCH=CH2)3. Aust. J. Chem. 2015, 68, 1342-1351. (41) The J values given for virtual triplets represent the apparent couplings between adja-

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cent peaks, and not the mathematically rigorously coupling constants. See Hersh, W. H. False AA'X Spin-Spin Coupling Systems in 13C NMR: Examples Involving Phosphorus and a 20Year-Old Mystery in Off-Resonance Decoupling. J. Chem. Educ. 1997, 74, 1485-1488. (42) This coupling represents a satellite (d, 195Pt = 33.8%), and is not reflected in the peak multiplicity given. (43) FAB, 3-NBA, m/z (relative intensity, %); the most intense peak of the isotope envelope is given. (44) The ortho proton signal was assigned by analogy to that of trans-6c (two downfield signals due to restricted Pt-Cipso rotation, δ 7.38 and 7.08, 2d, 3JHH = 7.0-7.2 Hz).4b The chemical shifts and multiplicities of the meta and para proton signals are also in close agreement. (45) The signal for the ipso phenyl carbon atom was not observed. (46) The PCH2CH2CH2 1H and 13C NMR signals of cis-7b and fac-10c were made by 1H,1H

COSY and 1H,13C{1H} COSY experiments. The corresponding signals of fac-11c, fac-

12'c, and fac-13'c were assigned analogously. (47) Schmidt, S. P.; Trogler, W. C.; Basolo, F.; Urbancic, M. A.; Shapley, J. R. Pentacarbonylrhenium Halides. Inorg. Synth. 1985, 23, 41-46. (48) The exact mass of the most intense [M]+ peak should be 1034.56. It is presumed that the instrument, which provides masses to the nearest whole integer, rounded the value down, and thus it does not represent the ion [M − H]+. All peak assignments were checked versus the theoretical isotope envelope pattern. (49) The situation with this ion is similar to that described in footnote 48. (50) These dirhenium peaks deviate by as many as ± 3 mass units from that expected for the ion given. However, the isotope envelopes are otherwise in good agreement with those calculated. (51) The situation with this ion is similar to that described in footnote 48 (calculated exact mass of most intense [M]+ peak = 994.42; the instrument is presumed to have rounded the value up, such that it does not represent the ion [M + H]+). (52) The situation with this ion is similar to that described in footnote 51.


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(53) One peak of this triplet is obscured; the chemical shift and coupling constant are extrapolated from the two that are visible. (54) This reaction was carried out with a Fischer-Porter bottle and H2 (5 bar), instead of a balloon pressure of H2 (1 bar). (55) Macrae, C. F.; Bruno, I. J.; Chisholm, J. A.; Edgington, P. R.; McCabe, P.; Pidcock, E.; Rodriguez-Monge, L.; Taylor, R.; van de Streek, J.; Wood, P. A. Mercury CSD 2.0 – new features for the visualization and investigation of crystal structures. J. Appl. Cryst. 2008, 41, 466470. (56) Lichtenberger, D. L.; Gladysz, J. A. New Author Guidelines for 2014: A Format for Computational Structural Data That Can Be Opened with Freely Available Programs such as "Mercury". Organometallics 2014, 33, 835-835. Table 1. Key crystallographic bond lengths [Å] and angles [°]. Pt-P Pt-Xc P-Pt-P P-Pt-X X-Pt-X

cis-1f 2.256(2) 2.263(2) 2.352(2) 2.354(2) 100.27(9) 83.94(9) 90.72(8) 168.69(8) 174.59(8) 84.94(9)

cis-2c 2.2507(14) 2.2563(14) 2.3661(14) 2.3689(14) 104.37(5) 83.23(5) 84.98(5) 170.65(5) 172.35(5) 87.42(6)

cis-2fa 2.250(3) 2.231(3) 2.345(3) 2.373(3)

cis-6c 2.3188(6) 2.3204(6) 2.056(3) 2.070(3)

cis-2da 2.2506(18) 2.248(2) 2.351(2) 2.774(19) 104.59(7) 83.42(7) 84.17(7) 171.22(7) 171.97(7) 87.82(7)

cis-2da 2.258(2) 2.2492(19) 2.360(2) 2.371(2) 104.70(7) 83.66(7) 84.23(7) 171.07(7) 171.61(7) 87.42(7)

cis-2fa 2.245(3) 2.243(3) 2.347(3) 2.365(3) 104.66(11) 83.52(10) 84.08(11) 171.22(10) 171.66(11) 87.77(10)

cis-5aa cis-5aa cis-5bb 2.2138(7) 2.2167(7) Pt-P 2.209(3) 2.2248(8) 2.2191(8) 2.3509(7) 2.3455(7) Pt-Xc 2.352(3)d 2.3548(7)d 2.3492(7)d P-Pt-P 104.29(11) 105.00(2) 100.11(3) 99.37(3) 91.07(16) 83.17(11) 85.66(8) 82.84(3) 83.99(3) 84.13(11) 86.10(7) 88.73(3) 89.38(3) 91.17(13) P-Pt-X 171.36(11) 168.08(8) 170.85(3) 171.15(3) 172.7(1) 172.23(11) 168.45(7) 176.87(3) 175.77(3) X-Pt-X 88.51(11) 83.61(10) 88.29(3) 87.21(3) 87.5(2) aValues for the two independent molecules in the unit cell. bA C symmetry axis renders the Pt-P and Pt-X bond 2 lengths and other parameters equivalent. cDistances from platinum to the ligating atoms of the non-phosphine ligands. dThe phosphorus-oxygen and oxygen-carbon bond lengths in cis-5a,b fall into the ranges 1.557(2)-1.593(2) Å and 1.432(17)-1.475(4) Å.


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5 TABLE OF CONTENTS GRAPHIC


Three Fold Intramolecular Ring Closing Alkene Metatheses of Square

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