Liquid nitrogen

The chemicals were purchased from the following sources: Karstedt’s catalyst (platinum(0)-1,3-divinyl-1,1,3,3-tetramethyldisiloxane complex (Pt₂(dvs)₃) solution in xylene with 2% of Pt), calcium hydride, platinum(IV) oxide (surface area ≥ 75 m²/g) from Sigma-Aldrich (Saint Louis, MO, USA). Sodium and benzophenone from Acros Organics (Geel, Belgium). Polysiloxanes: Cross-linker 101 (PS1, 4.3 mmol/g Si–H content) and 120 (PS2, 1.1 mmol/g Si-H content) from Evonik (Darmstadt, Germany). ((IPr*)Pt(dvds)) (IPr* = 1,3-bis{2,6-bis(diphenylmethyl)-4-methylphenyl}-imidazol-2-ylidene) and Mono(alkenyl)functionalized silsesquioxanes were synthesized according to the literature [101 (link),102 (link)]. Toluene, tetrahydrofuran (THF), chloroform-d, molecular sieves type 4 Å from Chempur (Piekary Śląskie, Poland). Argon and liquid nitrogen were obtained from Linde Gas (Kraków, Poland). All syntheses were conducted under argon atmosphere using standard Schlenk-line and vacuum techniques. Toluene was dried over CaH₂ and THF over Na with benzophenone prior to use and stored under argon over type 4 Å molecular sieves.

The following
isotopically labeled standards were synthesized as previously reported:
(¹³C₄)-butane-2,3-dione,^{29 (link)} (²H₂)-butanoic acid, (²H₂)-δ-decalactone and (²H₂)-δ-dodecalactone,^{30 (link)} (²H₃)-ethyl butanoate,^{31 (link)} (²H₃)-ethyl hexanoate and (²H₃)-hexanoic acid,^{32 (link)} (²H₂)-3-methylbutanal,^{33 (link)} (²H₂)-3-methylbutanol and (²H₂)-3-methylbutanoic
acid,^{34 (link)} (²H₃)-pentanoic
acid,^{35 (link)} (¹³C₂)-2-phenylethanol,^{36 (link)} (²H₃)-acetic acid, and
(¹³C₂)-2-phenylacetic acid were purchased from
Sigma-Aldrich Chemie, and (²H₇)-2-methylpropanoic
acid was from Merck.
Diethyl ether, sodium carbonate, sodium
chloride, and anhydrous sodium sulfate were purchased from Merck.
Liquid nitrogen was obtained from Linde (Munich, Germany). Diethyl
ether was freshly distilled prior to use. l-Norleucine and
4-methylumbelliferyl butanoate were obtained from Sigma-Aldrich.