Reuben tried the one guarantee that could possibly move his father. Targum Pseudo-Jonathan on Genesis 42:37 preserves the oath: "Slay my two sons with a curse if I do not bring him to thee. Give him into my hand, and I will restore him to thee."
The oath that could not land
Reuben offers to stake the lives of his own two sons, Hanoch and Pallu, as collateral for Benjamin's safe return. The Aramaic paraphrase, which took its final form in the Land of Israel around the seventh or eighth century CE, preserves the extremity of the offer. Bereishit Rabbah 91:9, a commentary on Genesis compiled in the Land of Israel around the fifth century CE, reads the proposal as earnest but tone-deaf. Jacob's response — captured in the next verse — does not even acknowledge it. Rashi (1040-1105 CE) explains why: Reuben's own sons are also Jacob's own grandsons. Telling a grandfather that his grandchildren can die if the plan fails is not a comfort. It is a second threat.
The oldest brother trying to lead
And yet, there is something genuine in Reuben's offer. He is the firstborn who failed at the pit in Dothan (Genesis 37:21-22). He is the oldest who has never led. Here he is trying, clumsily, to become the man his father needs. It is Judah, later (Genesis 43:9), who will find the right language — offering himself, not his children — and actually move Jacob to release Benjamin. But Reuben tried first, and the Targum preserves his attempt.
The takeaway
Good intentions fail when they speak the wrong language. Reuben wanted to save his family; he just offered the wrong collateral.